They have a mindset that gets excited when they find evidence, such as aromas, of a sexually receptive female. For male mammals, that evidence is a signal . Second, humans differ from lower mammals in having lustful ideas as well as desires. Men not only desire receptive women, they have ideas about what constitutes evidence that a woman is receptive. And they need evidence because women do not have the estrus or heat that results in the periodic sexual aromas and sexual swellings that go with animal receptivity.
Women are mostly free to have sexual desires and ideas whenever they want to.
So, in societies where women normally cover their bosoms, men's sexual mindsets suggest that a woman with bared breasts symbolizes a sexually receptive female. I'm not sure I get that. It starts with projection. You know, like a movie projector. When he sees an attractive woman wearing not much, or wearing clothes that reveal rather than conceal, Jesse projects his nonconscious belief that a women whose body is exposed is sexually receptive.