When I go out with male friends they don't even look at average fat or old women. Attractive, social, young and elegant women always get all their attention. Sure, most men (and women) will soon or later have to lower their standards to even get a shot in a stable relationship, but that is a slow process that does not need to happen more than a few times to be effective. That does not mean men would "fuck anything". Plenty of men lose sexual interest in the women they marry or get "Erectile disfunction" that magically disappear if they get another better looking woman.

As everything, there may be exceptions, but most men who would "fuck anything" are probably playing a numbers game for their own ego, no different from those "polyamorous lovers" that are just plain ugly nerdy people masturbating with each other's bodies (not judging, of course).

By the way, I don't find this dynamic as unfair to women, as women are as unfair when choosing men for their money or resources. The dating game is not and was never fair, but it is false to assume that men would "fuck anything".

TLDR: Just because men are generally hornier than women that does not mean they would "fuck anything" unless they have a numbers game to get some status or self-steem. That idea is female fantasy to feel better even when their bodies are not in the best shape.