If you really look, most of their identities have been revealed online in some places. They're almost always exactly what they sound like. If it's Hololive, they're in contracts and all that jazz, so they couldn't catfish even if they wanted to.
Like anything else on the internet, people will find info they're looking for if they look hard enough. It's considered disrespectful to the content creator's privacy to air that info out, but people do it anyway.
Yes, anyone can create a VTuber model and use a voice changer (heck, I know a girl from Discord who created her own and is looking to do it independently), but if you see any channel associated with names like Hololive, Nijisanji, or VShojo, those are legit people just trying to make a living working for those companies, similar to talent agencies and whatnot. There's no voice changers used in those instances. What you hear is that person's real voice (I say person, because there are male VTubers as well), though they may speak a little differently to be in character.
I don't really branch out much with the ones whose content I like most, but the biggest appeal for me is chill streams and good music. I don't interact with the fandom much either because of how the majority of folks act, but I do know a few online friends who are into it as well, so that's nice. It's not for everyone, but I think it's a neat new way for entertainers to work w/o the pressure of having their face be public.