1) Hololive hasn't been resting on its laurels. There are official Hololive games, there's that MMO that's being developed, they're working on their own streaming platform and so forth. That you can't even do a cursory amount of research or even ask basic questions to learn any of this seems more of a "you" problem than a Hololive problem.Depends. Holo started all about music and idols, so bigger and better annual fests is logical conclusion.
You can launch own clothing brand, you can hire good writers and make games or anime with your lore...
"outstanding" would be vtuber MMO, could be fire if you won't try to overdo it (think RO with higher res sprites)
"outstanding" would be penetrating normies market worldwide with your merch and stabilizing there (clothing)
"outstanding" would be hosting esports tornaments that rival blizzard
Though music events seems to be least effort tbh. "outstanding" there would be actually big fest, stadium levels.
2) You're really taking for granted how much time and effort it is to run an event, let alone run an event seamlessly and without issue. It's great that Hololive is running so well you don't realize how much work is involved with these events, but there is actually a lot of work and planning involved. There are plenty of examples of live online events going badly, even at a smaller scale than what Hololive runs, that you really shouldn't take this for granted.