Nice guys get a bad rep from delusional people who have it in their heads that all women want is some guy that's going to wreck their hearts and their lives. Oh please. Look around at every single women's magazine and on this site alone at how many complaints there are about these types of guys.
Women do want a nice guy. They want someone who is going to remember their birthday, and treat them with respect, and show up when they say they will, and not cheat on them. Typically this is the guy they marry because he is in fact, a nice guy who does all those things and ticks all those boxes, and I'd say the same is true for the person guys eventually marry.
I hate to hear that nice guys feel the need to turn into a-holes because they think that appeals to women. I think when you think you have to change everything about who you are for someone else, you're already starting off to a terrible start because how long can you keep that up before you truly become a real life a-hole which gets talked about like the trash they truly are.
Just as there are guys that go after the wrong girl, of course there are girls that go after guys who treat them like crap. Maybe they have a pattern of abuse in their lives or extremely low self-esteem. Some you can save, and some you can't for either guys or girls in terms of breaking this pattern, but don't let some convince you that all are like that or can't see that you aren't like "all the rest."
If you are a nice guy, remain so. You're looking for a quality girl among the riff raff who appreciates that about you because that is who you are. Don't change because some idiot doesn't realize she's got a good thing right in front of her because while you're wasting your time and efforts on someone clearly not worth it, there are still a lot of women who are out there looking for you and want you in their lives because they know dating a bad guy will only land them in a place where they are unhappy and hurting.