The stock prices are not great all things considered- I think that the vtuber audience needs something new/different to broaden beyond it's current market base AND I think investors would rather put money into AI related stocks than IP/vtuber related stocks.
Did I say 1950 pop stars popularity was authentic? I'm just saying the implicit question of this post's title can be simply answered with "they're so popular because of marketing, duh"
Which makes their popularity as organic as the explosion of the K-Pop mania.