I think there's multiple angles for this. When Haachama does her cooking videos, she's careful to not even show her hands, because even doing that could break the immersion for some people. Which I agree, is very unsettling to me.

However I think the reason that most people don't like seeing other projects from the same vtuber is not because they don't want to see them as a person, but because the Japanese take internet anonymity really seriously. Harassment online in Japan, especially of idols, gets extreme to the point of being dangerous. It's very, very easy to find the faces of some Hololive members on old Niconico Channels, however current fans lose their shit when you mention this because they see it as an attempt at doxxing. It's from a place of love, I don't think it is an attempt to dehumanize.