Pretty much this. I thought it was stupid at first, but all titty streamers do is let their tits hang out. Vtubers, surprisingly, require a good voice and personality to keep people going, because otherwise you're just looking at an anime girl.
Titty streamers require no talent and have a bunch of thirsty betas thinking they're going to be this girl's girlfriend. There's really no illusion of that with a Vtuber, because a lot of them you don't know what they look like. And hilariously, if you're good at it or have a decent voice, you can just continue to be a Vtuber after e-girls hit the wall and everyone moves on to someone younger. Since it requires some modicum of talent and has no requirement on looks (just cash money for a good AV) Vtubers make these bitches SEETHE and its fucking hilarious. They get so fucking mad its great.