Well, my own bias is because it's seen as depraved/pathetic if a man has an AI fantasy girlfriend which gives him a proxy of what he wants, but it's not if a woman reads her bodyweight in romance novels per year. In my experience it's seen as pathetic for a man to use a proxy for his desires (see also the sex toy industry).

Another angle is go down the rabbit hole of online dating app disparity, women (under a certain age and bodyweight) can have a short term boyfriend and attention essentially immediately and in an unlimited manner. Partly driven by coolidge effect in men's sexual desires (men as a group have near unlimited desire for novelty and therefore consume any/all available supply except that which is not generally/widely desirable).

Women already have a near proxy too. OnlyFans or an IG + cashapp account can mean she gets more from men than she could one man, and gives less that a wife would have had to in the past. An AI Boyfriend would have to give the things that women (on average) desire from men, which tends to be more like protection, resources/money, and status/social dominance.

AI Girlfriends work because men tend to be driven towards visual things, and novelty.