Gen "unity" only last so long until you find other people you connect with better outside your gen. So eventually Gen only collabs become less and less common. On top of that different goals also divert from Gen unity.
For example Fuwamoco wants to be big in Japan so they hang out with the JP crowd alot, but no one else in Advent cares about that. So Fuwamoco has to hang out with the JP crowd on they own. Bijou somewhat wants to be popular with the JP crowd, but is not putting in the effort on the level of Fuwamoco. And at the end of the day she just connects better with Kaela than any of her genmates.
Shiori wants to hang out with Homos, but of course no one else is gonna join her in doing this so she has to do it alone/with holoID. Nerissa wants to do the singing stuff and would rather have her gay ass family on stream than fellow Holomen, she also doesn't like games that much so she her collab options are slim.