森から出てきたばっかりでAFなんて見たことないので着方わからない説
逆に彼女達らしくアレンジして着こなしてしまう説

Idea: they just came out of the forest, so they've never seen Artifact armor before and thus don't know how to wear it
Alternate idea: they arrange it in their own way and wear it stylishly