we don't start out as dickheads
You get what you ask for
Not all men are dickheads!
The fact is that many men are not dickheads; but women seem to be drawn to dickheads. The result of this is that men learn that to be successful with women we must become dickheads.
It's not all that easy to be an asshole when we are not assholes or dickheads by our nature; but if we want to get good women we have to work at it.
We start out as nice guys but then we are either ignored or accepted as "just friends", which is worse than being ignored. But as friends we get a glimpse into the ways of women and we see that they all want dickheads for boyfriends. (At least all of the women we are interested in.)
So we start to be a little prickish and we get further. With this clear message we become pimples and life gets a little better so we graduate to buttheads. Now we are getting dates and having some fun so we move up to being boners.
Then after years of guidance, by the very women who will later call us dickheads, women we finally become dickheads and life is good.
I think the real question is why do bitches want only dickheads?
In the end you get what you ask for.