This has always struck me as odd. Breasts aren't technically sex organs. And as five minutes on the internet will tell you, there isn't a single body part someone doesn't fetishize. No one outside of Saudi Arabia seems worried that a glimpse of a bare ankle will drive foot fetishists wild.
When I lived in Europe, I spent a lot of time on the beach. It was very common to see topless women of all sizes and ages. It's startling for all of ten minutes. Then it becomes as normal as seeing shirtless men.