Same reason for what I wrote above.
I'm not saying that any individual TW consciouly comes up with this stuff.
We all know that the constant messaging of men are like this and we women are like that has massive impact, is insidious.
Women do this with men all the time as well when an easy answer to a question that's not comfy is just so much better.
With men when it comes to women it's really pushed hard, constant, and society nods along. And it overlaps strongly with porn of all types from soft all the way through. And so is intertwined with that basic drive. For most reinforced through puberty surely, when most young men are extremely, can I say frisky? I'd think associations reinforced often, and at that age. Will generally take pretty deep root.
The fantasy of women as doing everything to be sexually appealing to men, doing so much for men's approval. And more than that. Being so constantly up for it that they even get turned on eating chocolate (or feeding the cat wtf). I mean that's going to be irresistible!
From the that men know women better than women do. The skies the limit! And leads to do much- in this case- the superimposing of the idea there's constant competition between women (that's why they are all bitchy). The women with the things that are currently 'sexy' for women win. The other women admire and despise them.
In this case the belief that women have a hierarchy of social cachet (in general and ubiquitous) based on things like breast size is obviously ludicrous if stop to think about real life and women they know etc.
And yet. It's a male centred flattering view, which also dismisses women as being essentially all the same and shallow and living for male attention.
They don't WANT to know. To the extent that must never stop to think about it, or accidentally listen to things that day otherwise. If they do it's said by bitter flat chested lesbian feminist maniac. Simple!