It's about supply, demand and what's actually in demand to begin with.
When men see a woman with a tight ass they think, "Damn. I want that".
When women see a man with a tight ass they think, "Damn. I want that. I wonder if he has a good job. Does he pay his bills? Can he protect me in a dark alley at night? I wonder how he is around kids. Does he call his mother?".
Men want a tight piece of ass. Women want a package deal.
If you put a hot woman in a room of 100 men, all 100 men would want to hit that, but that woman would only look at maybe 5 guys as potential suitors. The other 95 men are screwed.
If you put a man who is the package deal in a room of 100 women, all 100 women would want that man, but there would be about 5 or 10 women he immediately wouldn't touch with a 10 foot pole. The other 90-95 women will probably get laid.
However, if you add a relationship into the mix, then things even up a bit. That package guy will also only look at maybe 5 women or so as likely suitors; women who have more than just a tight ass going for them. The other 90-95 women will be eliminated over looks, red flags and/or general bat-sh*t craziness.