A lot of replies here ignoring the obvious - patriarchy, religion, and capitalism.

I’ll be honest, if you don’t have an understanding of how deeply these (along with white supremacy, cis heteronormativity, ablesim, classism) impact not only society at large, but our individual choices (or lack thereof), and it sounds like you don’t, I can’t really help at this point, there’s just too much to unpack and it’s not work I’m interested in doing for you.

As for your ulterior motives - the first is easy to resolve by opening a search engine and looking it up, the second absolutely makes you sound like a creep, and also provides a perfect demonstration of the kind of external pressure we face that more often than not compels us to cover up - we feel you “appreciating” our “pups” (aka your “male gaze” or simply you objectifying us). And it’s fucking gross.

Maybe you should read my first reply again, this time try and actually listen to the experience of a person explaining to you the pressures they and others like them face from society that you never have, instead of dismissing it, and then invest some of your own time actually researching the topic, not of why people wear bras, but of how fundamentally social constructs impact society and all the individuals in it, and maybe you’ll start to get an idea of what the actual answer to your question is.

But I have a feeling you’re not interested in doing any of that, so I’ll just leave you with this - boobs don’t exist for you.