Nipples are a weird sexualised preoccupation in the UK. Where I'm from, bras are for
a) large breasts which require support for the comfort of the woman herself
b) achieving a sleek outline for special occasions
c) dressing up 'sexily' for a partner
Women don't feel compelled to wear bras day to day, irrespective of breast-size. Nobody would bat an eyelid at a woman's nipples being contoured through the fabric of her top or blouse. Not at work, in the street or at the gym.
When I arrived in the UK, this is one of the things I was struck by early on. Men -colleagues, shopkeepers, strangers in the street‐ would literally stare or comment, even though I was quite young and clearly not trying to 'parade' my boobs. I quickly learnt to comply and have worn bras ever since, in order not to cause offense. But I really hate it and definitely don't need to wear one.