So there is a fascinating historical rabbit hole here that I went down a few years ago. I think it is Nicole Rudolph who did a deep dive video into the history of bras and other shapewear. If you smoked a lot and like history I recommend it.
Bras and similar garments give the proper ‘shape’ for the clothes and cultural norms of the moment, and give people comfort and support if they need it. Lots of people need something sturdy to keep everything in place, but it’s also still a very grey area of social acceptance to choose not wear one.