Oh I can answer this! I watch quite a lot of VTubers, almost all of them from the Hololive brand and a few indies. I don't watch regular streamers anymore.
- The most succinct way I can describe it is it has some overlap with the appeal of the anime/manga subculture in the West. Imagine a character in an anime has a "soul" imbued in them and they talk for hours on YouTube about a brand of ketchup they like and all the specific reasons why they like that brand. Depending on the topic, it's hard for some to get enough of that sort of thing. You feel a sense of (parasocial) connection to the streamer as you get to learn more about them in these hyperspecific ways over the years, in a way that a static, deliberately constructed medium such as anime or manga cannot express. Accumulated personal knowledge of the streamer is the social currency of VTuber fans, and by extension fans of real-life idols, as it can only be gained by watching and following them for a long time. I would recommend the book Idols and Celebrity in Japanese Media Culture for an academic perspective of real-life idols, since many of the concepts overlap with Japanese corporate VTubers.
- Many anime/manga franchises and brands like Vocaloid have historically appealed to a need of emotional connection in the past with things like character goods, but VTubers interact directly with their audience so the effect is much more pronounced. It is like those characters are actually speaking to you for once (though usually they aren't speaking to anyone in particular). Plus they talk about their own favorite anime, manga and games. This is very appealing to some.
- An added benefit to watching VTubers that are part of a corporation is you get to see them interact regularly with the other members, which becomes a large part of the appeal. It makes it feel as if you're watching one cohesive group of friendly individuals, and you can also switch between watching different members if you feel like it/the schedules overlap.
- I don't know about regular streamers, but with VTubers it's a surprisingly social activity. People are encouraged to create art and post it on the hashtags of each streamer, so watching streams is a wellspring of motivation for creative types. A lot of the things depicted in that art would be unusual or weird if they were drawn for real-life streamers IMO, but in the VTubing sphere it is seen differently. I would say the vast majority of VTubers aren't insulted if you post something explicit of them so long as you keep it off of the offical channels. They will just ignore it and carry on. There is something to be said about this in a culture that some might say is becoming more and more puritanical.
- The fan communities are niche but very devoted. The people I've met through them have helped me in a lot of ways, and I have also managed to give back as well. Being a fan gives you a sense of identity. Meeting with a fan that watches the same streamer instantly gives us a lot things to talk about. Multiple people I met at in person events have described the community as "home" to them, maybe same as football fans are with a favorite team. People wear the liveries of their favorite streamer or cosplay and group together for large gatherings or do online fan activities. I'm not aware of an equivalent for someone like Asmongold!
- In Hololive's case, it is a truly apolitical streaming experience, I believe one of the few that exists with their level of popularity. I watch VTubers to shut out the chaos and cynicism of the rest of the world. You can depend on Hololive for this anti-cynicism bubble because they have stringent rules that politics or inflammatory topics are off-limits. Instead of feeling that it's restrictive, I would say it's a breath of fresh air. But in addition, the VTubers themselves are just fun to watch. Reading the interactions they have with each other online is one of the few times I get the "old web" feeling that has mostly vanished from modern social media. It is a precious feeling and I end up wanting to protect and cultivate it.
- With Hololive in particular, it's hard to describe but after watching for a while you get a "feeling" for what brand identity the management is trying to build, and that identity appeals to me. It is built on some level of restrictions on topics/activities (permission to steam certain games being one example) but the trade-off is the amount of resources thrown at each VTuber means they are freer to be themselves within those limitations and they don't have to act outrageous all the time to get attention, since the company takes care of promotions and reach. This one is big for me. I disagree with the article's notion that "eccentric", "expressive" and "weirder" necessarily contributes to a more appealing stream environment. A lot of those things mean being loud and attention-grabbing if you're an indie with no support to stand out in the overcrowded market, which quickly loses its appeal to me.
- Being a fan gives me an excuse to feel like a child again, without the feeling of being perceived as weird or a loner. I think this is common to a lot of hobbies. I can carry around a plushie of a VTuber I like in public and people have randomly come up to me an said "oh! Is that ______?" and we can hold a sustained conversation for like half an hour.
Wanting a sense of togetherness is why I keep returning. True, it is an experience based on a false sense of connection with the streamer, but I have made a lot of real friends in the hobby and we talk regularly.