A decent number of women might be attracted to alpha's, but that doesn't mean they're going to pursue them. Not all girls want who everyone else wants, and all that nonsense. A lot of girls will not date players or jerks. It's the female players and jerks we seek after that leads us to believe this. You know, the hot chicks every guy wants. That's all they focus on, and that's all they see. It's not all women - only the ones they are attracted to. Women are douche bags, too, you know. Just because they complain and blame everyone else doesn't change the facts. Nobody wants to be perceived as a bad person, and will throw the blame on others. A lot of these alpha / jerk lovers are the same way themselves.
This usually occurs during the younger years, and us men are guilty of this, as well. We all want the trophy girl that everyone else wants, so we can show off, and look cool in front of our peers. Status and popularity is at the forefront during high school and into the college years. A lot of that changes as you get older, and you realize these hot chicks / alpha males aren't worth the trouble. They're just fun. Most people end up getting involved in and married to decent, nice folks. I see decent, nice couples EVERYWHERE. They far outweigh the bad ones. A lot of girls are also interested in nice guys (though not in the stereotypical "nice guy" sense).
It's those younger years, and the kind of people you are attracted to during this time, that messes people up, and gets them caught up in this whole alpha / bad boy / jerk / douche bag theories. A lot of guys seek after these young, hot girls for some time after the college years, so the stereotype never leaves. They're still going after the same type of person that caused it in the first place. Even if the girl isn't young - she's still the same kind of person. Some people never change or grow up. And some people never stop seeking after this kind of person. Familiarity, wanting to finally catch the hot chick and feeling good enough, etc.
I think a lot of people who seek after the alpha / hottie are really just battling with their own ego, and wanting to be accepted by society in general. Or, they think this time is going to be different - they're older and wiser now. What they don't understand is, these people are never going to change. They don't usually like the person at all.