I don't see why you'd have to go for a fat chick when you're not fat yourself.

Because male libido > female libido. So one very good looking man can satisfy many decent looking to good looking women in modern hookup culture. This partner selection crowding pushes all the way down the SMV scale. Average non-fat guys often find nothing left except fat ladies. There's your answer.

Also, hooking up with too many alphas harms LTRs later. If you're female and you don't believe, try flipping the genders.

Imagine if your future husband had grown up in a remote village with 10X as many females as males. He had his pick of dozens of 105-125 lb gymnasts and cheerleaders practically since puberty. Now years later he moved to the States and he's married to average, ordinary you. How long do you think his attraction would last?

Now imagine a world of high earning women who almost always have to pay alimony to their lower earning ex-husbands when they bail out on them 80% of the time. The men are almost always awarded custody of the children because of the recent rash of female sex offenders, so the ex-wives also have to pay another few thousand a month child support. Hello, shitty apartment and retirement at 75.

Have a noisy verbal argument any time during the marriage and the neighbors call the cops? You're automatically going to be arrested because women commit 70% of domestic violence and the cops finally figured this out.

Now, would you marry?

tl;dr Women have spent so many decades complaining about the "partriarchy", they don't understand the world they're living in.