I think based on the environment they have grown some people feel like babies even though they are over 20 or some feel like mature & serious even though they are minor. Actually I don't stan any group that most members are younger than me. It feels uncomfortable. But for TREASURE they feel most familiar to me. Since I am only child and grown alone I have always wanted to have baby sister or brother. TREASURE just feels like my baby brothers. So I can't help but babying them with a heart of big sister.
I swear if that isn't 99.999% of the fandom.