First off: EzzyB, if you're reading this, please don't consider this a slight against you or your story, because it's not. I thought it was very good, even with its flaws. Besides, I've fallen into the same trap as well. That's kind of the point. Also, some of this—maybe a lot of it—is influenced by a discussion of similar topic over on the SOL forum, so, apologies to all of you if you feel plagiarized. It was totally not intentional.
Now, to business.
Those of us who write and post on the erotic-fiction sites are in a very particular niche of fiction. Specifically, we write sex stories. And one of the main elements of sex stories is escapism. I personally tend to write very realistic sex, but 1) I'm in a minority, and 2) I get criticized for that. Evidently, The Reader doesn't want realistic sex scenes with elbows and awkwardness flying around everywhere, and Caitlyn trying out anal and discovering she just totally doesn't like it—and, if you think about it, that makes sense. Of course The Reader doesn't want that! He can get that every night from his wife! He wants something he can't get; he turns to porn for a different reason than just replicating his everyday existence.
So, as an exercise, let's take it to the obvious extreme: let's create the perfect Escapist Character. This male lead ought to be Brad Pitt handsome, in excellent shape, employed at a wonderful job that brings him tons of money, and endowed with cock and bed skills sufficient to bring any woman to ecstasy. He ought to be surrounded by scads of beautiful women, ones who are attracted to, oh, many things: perhaps his reputation. Perhaps his intense charisma. And the woman (or women, if we're doing one of those ridiculous threesome relationships; that's another rant right there) he ends up with should be unattainably attractive somehow. The exact specifics of this woman's personality and appeal will differ from story to story, or (more accurately) writer to writer; after all, we're all attracted to different things. But there will be something exceptional—and exceptionally appealing—about her.
And, of course, the male lead should not change. By which we mean, there ought to be no—or at least little—character development.
I can hear you going, "Now hold on a second, CWatson. Character development is one of the core aspects of any fictional excursion." And you're right. But think about what we're doing here. We're writing a story—words on page—but we're not necessarily writing much of a plot. We're here to provide an idealized, escapist fantasy to men all over the world. And what do men want? To be so superbly attractive that nothing about them needs to change.
(This begins the Grandiose, Sweeping Generalizations part of our program, but please bear with me.)
Women don't think this way. Women see men as works-in-progress. They know that people change—and, more pertinently, they accept the necessity of compromise. And they want to change their men; or, perhaps more accurately, they want to be so important to their men that the man is willing to be changed. That's part of where the All Girls Want Bad Boys" thing comes from. Cleolinda Jones has this to say on the topic:
But, remember, that's a girl's fantasy, best examined in Twilight. You and I are trying to craft a boy's fantasy. And the weird thing is, guys have the exact opposite desire. We don't want to be changed; we don't want to love someone for whom we have to bend our very natures. We're lazy. Instead, what we want is someone who loves us for exactly who we are, no alterations necessary.
Now we take this one step further: we turn the tables. A good story does need character development, after all; it adds spice and emotion to an already erotic story. And the thing about a sex story is that (unless you're writing a solo excursion) there's guaranteed to be a second person in it; sex is something that's hard to do with only one participant. So, it's obvious: the woman can change. And the man can be the instrument of that change. There's now a mentoring aspect to the story: the male partner helps the woman come out of her shell, become fully-fledged, be more herself... without any evolution on his part. All Girls Want Bad Boys... Reversed. Defrosting the Ice Queen—, or rather, in our genre, "Awakening the Sex Queen". (Whether being a nymphomaniac is against the female lead's nature is up to each writer; some like the idea of a maven who is ready to come out of her shell, and others like women who have to be coaxed. But either way, she learns to let herself loose, and the male lead is who gives her permission to do it.)
Thus: Static male protagonists. Why doesn't he change? Because he doesn't need to.
I've written stories like this. Brandon Chambers, in particular, has been in this position at times. But I fight it as strongly as I can. Why? Partially because it offers a rather embarrasing glimpse into my personality; every writer knows they can be psychoanalyzed via their stories, and is a little worried about what readers might find. But mainly I try to avoid this because it's bad storytelling. An idealized, unchanging, perfect protagonist? That's a Mary Sue, and generally one should avoid such characters; they're not only embarrasing, but they're boring. Interest in characters comes from seeing them overcoming their flaws... but starts from seeing them have flaws, identifiable ones that The Reader can empathize with. A lot of young people, for instance, have felt outcast, misused, under-tolerated. That's why Harry Potter appeals to them, or Bella Swan. The Reader likes to be able to reach out to their favorite characters, and empathize with them. They want to be able to say, "I know this person;" they want to be able to say, "I am this person."
And most of us aren't able to say that about a millionaire playboy with a cock the size of the Eiffel Tower.
Now, again, we're talking escapism here. Most of us cannot say that we're that person; but don't we wish we could? I mean, who wouldn't want to be a millionaire playboy with a cool car and all the other junk? Wouldn't it be awesome to have no problems in the world at all, and women tripping over us? I'm sure it'd be great to live... but writing about it would be kind of boring. Happy characters don't make for good fiction.
Now, here's the thing: these two situations aren't mutually exclusive. First off, it's possible to have a millionaire playboy with a cool boat, massive junk, and a Dark And Troubled Past (as long as it intrudes into the present; Ezzy, this is where I think you stepped wrong. Tony had issues, but I couldn't feel them at work in the present). Second off, even if you do insist that your male protag be a Static Character, he doesn't have to be that way all the time. Did anybody notice me doing this in "Naked In School"?—because I didn't either; it was just happening subconsciously: various characters would be Dynamic sometimes and Static at others. Brandon and Meredith get a lot of character development while at Mount Hill, but in "90 Days" they're both static characters, brought in more as recurring mentors than as central stars. Jane was Static in her first and second appearance, but Dynamic in the third and fourth stories... and then, in "When The Time Is Right", the story that's about her, she's a Static protag! (In fact, I re-gender-flipped the All-Girls-Want-Bad-Boys thing, turning Jane into the Static Male Protagonist who helps her lover effect change in his life!) Obviously, it's tricky to switch a character back and forth within the same story, but it can be done; and, if you do so, then your characters can have different roles at different times (and different responses too; this loops back to the "Wide Characters" idea I wrote about elsewhere).
But it's tricky. By and large, men prefer a perfect paragon to imagine themselves into; stories where those men make mistakes get huge amounts of negative feedback. (Remember the fan backlash Nick Scipio suffered when his protagonist started making mistakes?)
Can I—or even should I—tell you to always write nuanced and non-flat male protags? No. I can't, in good conscience, tell you that. Partially it's because you use different tools for different jobs. In a purely-escapist fantasy, a male protag with flaws is just as out-of-place as an ugly hooker. (Actually, more out-of-place, because she could be the unattainable main love interest!) And the simple fact is that purely-escapist fantasy works. There are seventy bazillion porn sites on the Internet and all of them make their money by providing that kind of escapism. Ethical concerns about "selling out" notwithstanding, you could do way worse for yourself, monetarily, than to pander to that audience. If you give them a perfect, flawless male protag for them to pretend they are for an hour or two, they will eat it up. Will it be a good story? Maybe not. But is your goal to create a good story?, one with literary merit? Or is it just to sell copy? Because if it's the latter (and we all must make money somehow), you should go with what works. Both approaches have their places. At least now you know what works, and why.