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Majority of the western audience rely on clips to get a rough idea of how their oshi behaves or acts. Hololive is easy to get into due to the large amount of translated clips. Even if you don't like one girl like Korone or Matsuri, there's plenty of dedicated translation clips soley based on one Holo most of the time. It's therefore very easy to get into Hololive because it has a stong translation community, which is in part because of the small bodycount for Hololive as a whole.
In comparision, Nijisanji has over 200 members, and most translators for Nijisanji take the approach of translating the "Best of Nijisanji" moments instead of focusing solely on one Niji and setting up a foundation for a fandom. Most people like Nijisanji, but they can't get into it because there's too many members to focus on and it could be literal months before your favourite gets featured in a clip, and even then there's no guarentee the clip will be that good.