>>97575549Hololive has built up enough brand loyalty and trust over the past few years for its community to go "oh, I remember that girl who collab'd with my oshi she was cool I'll check her out". Combine this with content like song collabs.
More importantly, it works for Hololive precisely because the girls are fewer in number. There is more time and space to focus on the quality of the relationship between them, as well as the room to allow them to branch out and make friend groups outside of their respective waves in a more organic way. Observing the way the friend groups diversified in HoloJP is the perfect example of this. In contrast with Nijisanji frequently vomiting out waves of talents, there isn't any time for the roster to stabilize and foster any real sense of rapport because they're constantly adding more NPCs and side characters in their efforts to filter out the chaff and find a new Gura.
You know the answers already, don't make me spell it out for you. I'm not even a holofag.