Altare Explains How The PPAP Song in Kobo's Karaoke Came About 

I can't get this out of my head🤣

well as far as i know, they (Holo and Stars) can do collab. but the fans(viewer) on each group have their own Fanatic and Anti. so it will be quite hard and dangerous sometimes if they do collab. Especially if they develop some close relationship that lead to Teasing or Flirting each other. Since most of the talent are aware of their mature stuff. But on Kobo case, it is little bit special. because since Kobo debut and until now, she still maintain the status and personality as Brat/Kusogaki, even in her real life. So most of Kobo fans know that how childish she is. it leads to the point that Kobo sees the holo stars which is MALE as Bros or as a gank to play around. and even the Holo stars fans see Kobo also as a brat (annoying Brat). For them Kobo will only go as far as Brother-Sister relationship. so it is quite acceptable, even for the Fanatic and Anti. But for the other Female Hololive it will be difficult, because they have MATURE personality. which can lead misunderstanding if they do collab with Holo Stars too often.

those fools fans always forgot that vtuber also a human being that need a socialize even with opposite genders