If you are in a clothing optional sauna where other girls are topless, why do you keep your top on?

I've been going to one for a few months. There are typical 3-4 who takes their tips off but most leave there's on. Seems like when normalized, everyone would want to especially in a sauna.
If you are in a clothing optional sauna where other girls are topless, why do you keep your top on?
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