If girls are only attracted to assertive, masculine "alpha males"...

Because girls are not only attracted to "alpa males". It's men who obsess about being an alpha male. Masculinity and assertiveness are actually not the most important qualities for a lot of girls. They may as well be looking for a smart and funny guy, for instance.

Some girls are actually turned off from alpha males because of their arrogance and want someone a bit more down to earth-esp if they want to settle down and get married. An alpha male will have too many women after him which means a lot of competition and rivalry on the girls hands from other girls. I've know girls wit really hot guys and some get told "oh you're so lucky" which makes them insecure. whereas if theyre with a more regular guy, then the guy will be seen as the lucky one. with a regular guy, you don't have every girl chasing them. Alpha males are usually very narcisstic and selfish. Whilst that confidence is undeniably attractive for a fling, it doesn't work for a relationship. They spend way too much time on their appearance. They turn on the charm for every girl so you kind of know deep down that you're not that special after all lol! That they could have the same effect on every girl. Whereas with a regular guy, you feel like they're a bit more real and not as image orientated. (basically that you can have an intellectual conversation with them). I think some avg guys wil try harder in a relationship than the alpha because the alpha knows he's got more opportunities so if this thing doesn't work out, then he's got his pick from the crop anyway. Also some average guys can be not great looking at all but just really funny. girls like sense of humour too and that humour will get them girls even if their looks wont! girls in their 20s will want an alpha because as we get older we realise "oh wait I want a serious relationship so maybe I should go for someone who treats me well ie not an alpha". Even if the alpha tries to treat the girl well and is nice, I always think that its always about him in his mind. I could be wrong though this is just my opinion!

because women don't all like the same thing and regular Joes can have qualities that a woman would want too.

thats like saying men only like size 0 barbie looking girls but 60% of americans are overweight and are still dating too

Well, there's a limit on the supply of alpha males, so that's part of the reason.

The more important reason, I think, is that the kind of guys that men have in mind when they think of alpha males are different than the ones women define as alpha males. I work with a lot of men and I'm often surprised at the things they do to make themselves more alpha-male-esque and more attractive to women. Because most women I know don't care about those things.

For example, a lot of guys go overboard at the gym building up their muscles. Most women I know like a toned guy, but they don't want a Hulk Hogan clone and they don't want a guy who seems to spend a lot of time trying to look good. Also, a lot of guys think that an alpha male is very rich and has an advanced degree. Women like financial security, but most of the ones I know prefer a guy who is interesting, enjoys what he does, is good at what he does, and is charming.

The regular guys you see on the street might not look as masculine as you would expect, but they are probably good at their jobs (women like to feel as if their guy is the best), know a lot about what is going on in the world, and know how to treat a woman. In other words, they are sophisticated. The pumped-up muscle guys and the wall-street type guys who have high-paying jobs are often pretty ignorant and lack charm. Many of them can't have a good conversation and only want to acquire stuff to show it off to people. That is not a turn on to many women. The world has changed and women don't need cave men any more; the alpha males have qualities that are more suited to today's world.

Because the drugs are working...

It's very simple if you think your self as the masculine, assertive, alpha male and act like it, then guess what women will think your the alpha male.

"If girls are only attracted..."

That tells you not all girls are attracted to these types.

To get along fine in the long run, likes attract, and stay with likes. If you see contradictions to this, look under the table, don't be deceived by what appears to be contradictory to your eyes.