Is it fair to say that people prefer Hololive over Niji because overall their talents have way more strong and unique characters where Niji is filled with milquetoast streamers that are literally dime a dozen. Maybe thats why they spam so many gens in hope to capture that one Pekora or Marine in the sea of mediocrity.
Honestly, there is no one like Pekora, Marine, Nenechi, even Rushia while she was still there, Fubuki, Matsuri, Coco (while she was there), etc. I cant name one Niji that makes me go "Holy shit I really wanna watch this person", and I did watch a bunch of Nijis over the years. Mostly Mito, Kaede, Noraneko, Hayama, Mao, Hakase, and Chigusa.
Incidentally, I think this is completely opposite on the EN side where Niji has more unique talents and stronger personalities where Hololive is just kinda...meh.