That's the problem really. The problem isn't that this is so complicated to understand. The problem is nearly all of us, at one time or another, wish that it was complicated, because we don't like the simple answer to the question, "Why isn't that person as attracted to me as I am to them?" We'd love there to be some complicated, intricate (and therefore hack-able) explanation, because nobody wants to hear the blunt, simple truth. If you're more attracted to them than they are to you, it's because you're ugly. Don't like the word, because you think it always means physically disfigured or something? Well, part of me wants to say, "tough." But fine, let me try to soften the blow (at the risk of it not getting through to you that I actually mean what I'm saying). It means that you're not attractive enough.
Now, we'd all like the question of "what's attractive" to be complicated, and therefore something that people who are attractive could teach us and then whoah, we'd understand the simple, easy thing we could do to be more attractive. Sorry. Not so. If you want the sexual or romantic attention of someone who's more sexually or more romantically attractive than you, then you're simply going to have to become as sexually or romantically attractive as they are. Nor is it hard to understand. It's just expensive, and more importantly, it's hard, boring, work. Exercise hard and eat right, whether you feel like it or not. Clean and straighten and whiten your teeth. Do something right with your hair. Dress better. Learn to listen to the person right in front of you, and practice other basic good manners -- nothing fancy, nothing obsequious, just basic good manners. If you're unusually stupid, illiterate, or uneducated, then fix that. Especially if you're a woman, address any crippling emotional issues that are obvious at 50 paces. Even more importantly than that, especially if you're a man, do whatever it takes to get a better job so that you aren't such a loser. Is there any part of that you didn't know? I didn't think so.
Nor, really, does anybody give a shit if these things are harder for you than they are for other people. Yes, the other person that you wish was attracted to you might not have to work as hard to be attractive as you do. Yes, you'd dearly love for there to be some way for you to work no harder than they have to and yet seem attractive. Tough. It doesn't work that way. Either do the work, or get over it and settle for people at your own level of attractiveness.
What's this got to do with "nice guys" and whether or not women find them attractive? Please. If you're not as attractive as the person you're attracted to, no amount of obsequiousness, and no amount of favors forced on her without her asking for them, is going to make you more attractive. In other late breaking scientific news, water is wet and the Pope is Catholic. And what's more, volunteering to be treated as a doormat for as long as it takes for her to feel guilty enough to fuck you in order to salve her conscience for treating you like a doormat isn't exactly "nice," either -- it's blackmail. If you're going to use emotional blackmail to make people more attractive than yourself fuck you, you might as well skip the emotional part and use a gun. OK, I guess that would be slightly more illegal, but I assure you it won't be any less obviously vicious or dangerous or disgusting to her; she's as likely to run away from your attempted emotional blackmail as she would be from an armed rape.
You're such a sensitive feminist, guy? Then you ought to have read, in one of your endless books, something about a classic bit of feminist theory called The Protection Racket. It goes like this. There are three kinds of guys in the world: Bad Guys, Good Guys, and Useless Guys. Useless Guys are useless. Bad Guys hurt women. Good Guys protect women from the Bad Guys ... but they expect the women to be grateful in return. If you did read about that, I'm sure you thought it was Neanderthalic. Too bad you didn't recognize that volunteering to be there for her emotionally after the emotionally neglectful or abusive guys stomp all over her feelings (and then hoping she'll be grateful enough to fuck you for it) is the same protection racket.