A lot of people who like vtubers are looking for ones that sound and act a certain way. This means the more high pitched anime types tend to get pushed to the top. People interested in becoming a vtuber see this, and then tend to imitate it. Repeat.

There is an element of the vtuber viewership that I will say behave incredibly inappropriately, and I think those people that seem to fetishize the "anime" elements can make the bad stereotype worse. I know a few people that went into vtubing, and the actual degenerate viewers are a real problem since there seems to be quite a lot of people that might be mentally unwell and can't separate their "anime fetish" from them interacting with a real person behind a fake face. It's like the people who talk to Woman in a very inappropriate way due to parasocial reasons, but amped up to an extreme level since they can't separate the fantasy from reality.