One of the things I noticed is the number of male-majority collabs in NijiEN is huge. I casually scrolled through some JP pages and found they didn't have as many.
So I decided to actually take the data and see if my assumptions were correct.
https://files.catbox.moe/rmj2xs.txtI found that NijiJP does plenty of girl's-only collabs, something that doesn't exist in NijiEN. They also typically split collabs evenly between genders, while NijIEN will do crazy gender ratios like 11 men, 4 women.
Pretty much the only way NijiEN gets an all-girl's collab
-- a 1v1
-- a wave collab
-- a collab with JP
Large all-girl's collabs of like 6-8 people exist in JP, but not in EN.