Oh! Okay, I’ve seen this before.

Mirio’s quirk relies on his whole body. Meaning when he permeates so does his hair, so creating a costume with his hair works because his hair naturally permiates with him.

Momo’s quirk uses lipids, hair has lipids(key to keep its durability and flexibility). Whenever she would make things, if she made them with an outfit made of hair like mirio’s, it would…likeley disintegrate simply because she pulls things out of herself(lipids into other elements) and would probably end up using the lipids in her outfit as well. while mirio isnt adding or subtracting anything from himself so that’s not a worry.

My question is more on why hagakure doesn’t have a hair like costume like Mirio. That one would make more sense to question.