Amazon is in the process of developing its own $10 bra, according to the Wall Street Journal (paywall). There's been a wave of online startups devoted to disrupting the lingerie space, once dominated by Victoria's Secret. Brands like Lively, ThirdLove, True&Co, among many others are offering women a wide range of options in terms of price, quality, and aesthetic.
When it comes to selling underwear, fit is perhaps the most important factor. It's unclear how much research and development Amazon has invested in creating these new products, but if they aren't comfortable, customers are likely to go elsewhere. Also, if they're Amazon-branded bras, they're likely to be competing with more utilitarian brands like Hanes, rather than Victoria's Secret, which has invested a lot in building a lifestyle brand around the products.