"If it were replaced with male genetalia I think that would be a little different purely because it's an image we are not met with on a daily basis, as we are with breasts. People feeding babies, changing at the swimming pool etc."
You are quite right, this is exactly why it persists - because you do see naked or near-naked women everyday.
That's why you think it's acceptable.
But please don't make me laugh about seeing breasts from people changing at the swimming pool or breastfeeding. That's a poor comment. Someone commented earlier that her friend was breastfeeding in a shopping centre and told to put them away by a security guard. Meanwhile images of naked women on the shelves in newsagents very close by.