>>1260095Part of it is that it's just a bit of a minor ongoing trend. A bunch of indies had been doing Duolingo for stream content, followed by VOMS, followed by Nijisanji, and now by Hololive. Duolingo is gamified, which makes it amusing to watch vtubers struggle through it. It also lets EOPs feel a connection to the vtuber since they can actually help (or feel like they're helping, among all the spam) through the chat for once. As an actual learning tool, Duolingo is kinda crap and doesn't prepare you for actual use of the language at all.
>>1260306Japan is an insular, self-sustaining cultural ecosystem. They produce enough of their own entertainment to not have to care about the rest of the world. They create and consume things tailored for their tastes, which don't always coincide with most of the rest of the world.
Imagine you were a celebrity in the US, producing content tailored for american audiences and making good bank off it. Would it keep you awake at night if you were less known in India? Brazil? Germany? Would you know, or care to know, enough about them to properly cater to them? Chances are you wouldn't feel any need to, the US is big enough of a demographic by itself. That's how Japan is for the japanese.
