If you get into the nitty gritty, it becomes obvious a lot of women follow these fatasses (obsessively in some cases) to feel better about themselves. It doesn't get much more complicated than that. They're not necessarily deriving laughter from these cows.
There's a thread in BP's Off-Topic that covers haters of Amberlynn, Chantal, so-on, and they show themselves to be no better than the women they mercilessly mock. The majority of the BP falls under that category themselves, however. They'll slip into that infuriating Twitter/Reddit talk and A-Log the living hell out of their subjects, as if they genuinely fucking hate them, moralfag ceaselessly. The board just goes to show that women, by and large, are not very funny and can't comment on lolcow without getting wrapped up emotionally. There're a handful of cool regulars there, but it's only because they're neutral.
I'm a woman myself. A lot of people have a hard time believing that, even though I think I present as one pretty blatantly. Nevertheless, if you're not talking like a ghetto, self-referential spaz in every comment, people assume you're a guy. I think it's annoying when you can obviously tell it's a woman typing. Maybe that's misogynistic somehow? Anyway, BP is full of women just like that. They hate these fat girls because they're an outcome they're headed towards, and they have to prove to all of the internet strangers that they're "not like that!" by any means necessary. They might not PL that much, but they are incredibly vitriolic.
You're right, though. I don't know how anyone can sit there and watch a 12-minute-long video of a Deathfat eating disgusting food. Hell, just playing a Deathfat's content in the background is weird too.