Three years ago Kagura Mea did a stream to tell the honest and brutal truth about corporate vtubers (Holo/Niji), since she knows them and they even tell her this stuff
1. If they talk about being sick on twitter and need rest to feel better, it's either to spend time with their boyfriends or vacation time for themselves. A lot of them will even sound sick/create fake stories of how they got sick to bait some SC or to guilty trip their listeners to supporting them
2. Some will play video games a lot because they hate interacting with their weirdo fans, even if they're not good at games, it's easy SC and they can just talk towards themselves while playing.
3. In discord, they have two voice chats. A professional voice chat where the vtubers will plan future events or run scripts with other vtubers. The other voice chat is OOC (Out of character) and yes, it's personal talk, girl gossip and they do make fun of your cringy or hate posts on twitter about them.
4. They're in it for the money, this is a business. It's not because "they love to make people happy", they're giving a service to entertain to help that brand and themselves get rich.
5. Some of the popular vtubers have great tricks with guilty tripping their supporters or even new people into giving superchats. From being a cute airhead that's too dumb to know anything or telling a fake sob story where they pretend to be social retards or super super shy in public and can only relate with their audience.
Example of the airhead: https://streamable.com/ji5kuw
6. If the vtuber acts "super lewd" or "I'm a degenerate like you guys", it's SOMETIMES just an act to entertain the listeners, they likely just did research on a couple of doujin artists to say their names on stream or say certain things based on what their audience say on twitter/chat (this DOESN'T apply to every girl because there are dirty girls out there)
7. Due to the restrictions from Youtube, the vtubers are unable to do more "racy" streams, which they really want to do to gain tons of red superchats. An example said was "Bikini 3D streams"
8. When a vtuber doesnt stream of Christmas, it 100% of the time means they are fucking their boyfriend.
9. Vtubers participating in FPS tournaments engage in massive orgies after the tournament is done. The members of the winning team has first dibs on who they want to fuck.