system
A chat on subreddit /r/NoStupidQuestions
human
It's more comfortable to have an additional layer between my genitals and pants.

And whilst I am a guy and obviously can't speak personally on this, I'm told that the main reason women wear bras is mostly because men would stare at their boobs even more if they didn't.
gpt
I hear that for some women, the main reason they wear bras is because they would constantly move around / cause back pain if not! Not because men would look!