>>596831
>Besides, beauty greatly differs from eras and locations. Nowadays people are very fond of huge breasts but it wasn't always like that. There have been periods where flat chests were the pinnacle of a woman's beauty.
This.
It's just secondary sexual characteristics, like bodyhair and less smooth skin for males.
It's considered hot due to cultural evolution, as >>596908 says.
Some tribesmen consider western obsession with boobs to be childish and hilarious, to continue >>596922 's argument.
And it's not like us guys are sophisticated fetishists, in general.
Show a saudi chick(that isn't even that hot under all those clothes) in some amorphous Niqāb, or some super modest female in general, and you know a lot of guys will want to plow that, despite it being really sexless.
While i love busty gals, i like skinny chicks much more.
tl;dr: it's mostly sexual memes, OP.
>>596849
Setting aside micropenis, small penises were also a fad in certain areas and eras of the world, and being less hung always has it's advantages, just like shopping more easily and not having back pains is something small-chested women admit to appreciating at times.