I just came up with a theory that probably a little on the crazy side (and possibly completely wrong), but I still feel the need to type it out.

I think the reason that girls are not attracted to the traditional "Nice guy" is deeply rooted in genetics through a process known as Natural Selection. If a girl were to fall in life-long love for a guy who would always be there for her there then that girl would have the distinct disadvantage restricting her genetic succession through that single guy. By falling for non-nice guys who are likely to leave them after they are done, girls are able to have more partners while still having the potential to eventually settle down later in life and marry a "Nice guy".

That is all.