>>54451907because hololive and stars are separate while nijisanji is one and the same. on the JP side at least, one could theoretically consume a good amount of hololive content without ever knowing the stars exist. you can't say the same for nijisanji, while some waves are female or male only there are mixed gender collabs and the big company events include both genders.
both are doing what works for them, hololive shouldn't do mixing and niji shouldn't try to separate the genders.