I can already tell this thread is going to go great.
If we want to gain an understanding of the vtuber boom that goes beyond calling them the spawn of the devil, we have to take a proper look at all of their characteristics and seriously consider what could make them attractive. Otherwise, you might as well dig your head in the sand.
First, the claim that they are simply LPers. There are a number of very important differences here: let's players don't put out songs, they don't go on concerts, don't go on seiyuu radios, don't appear in gachas, and, most important of all, don't appear in so many doujins.
So, why do they play videogames all the time?
First, a digression. You don't need me to tell you that when someone likes something, like say an anime, they often wish they had more of it. See: fanfiction, creating the content yourself. Videogames are a trivial way to pump out hours and hours of new content. The chat is key to the whole thing, they help set up situations that the vtuber works with to better entertain, a thing that is indeed a lot like regular streamers. But, you can see vtubers are far more character-centered than common LPers due to the prevalence of zatsudans and superchat readings to which thousands tune in to, in those streams there is no activity other than interaction and blogging. If people are attracted by them being good at games, that's more of a coincidental thing.
Now you may ask, what character? It's a real person. Absolutely true. Compared to a fictional character whose story must be written, the vtuber supplies their already existing story. The more unique parts of it are highlighted, as there is a charm in a fictional-sounding story being real, actualizing fiction. For example:
If someone, say, goes into an /ss/ thread and posts about how he had sex with his babysitter when he was 14, he's likely to get a standing ovation. Stories about your very real imouto are also likely to be well received. A relatively recent post in /ec/ commented about an artist and his failure to carry out his femdom fantasies. None of this is novel, it might be impure but it is what it is.Post too long. Click here to view the full text.