I am not arguing that this happens everywhere, in the same way and is then set in stone forever. People in different places and times had different circumstances. Hence, they could have chosen to handled things differently. Cultural norms can also sometimes change over night. Look at the sexual revolution of the 60-70s for example.

I was trying to answer the question where this norm comes from. Not why this norm isn’t universal.

It seems obvious to me that a culture that have normalized breasts in everyday life, would also consider them less sexual in nature.