Leaving the question open for guys too, because they might have suggestions.
Most Helpful Guy
I think it's because of the long standing culture of modesty that most countries have. I know that not wearing a bra doesn't necessarily show more skin but sometimes it can show more "motion" when you take that support away from some girls.
I think it's just a cultural thing. I don't think you should worry about it.
Most Helpful Girl
It's a messes up society we live in to be honest, lol