I said it once and I’ll say it again. The reason we get stuff like this so much in Japan is because the Japanese just find breasts funny just like penis’s to be funny. Boobs are the dicks of Japan.

I watched this one Gaijin Goomba video that also explained that Japanese society is not as reserved as certain Western cultures are when it comes to sexuality. Like Japan in general has been a culture that's very open to sexual expression and being open about it, while Western cultures, most likely as a result of the dominant religions in said cultures, has usually preached a more "reserved" sense of sexuality where it's treated as being more "private."

As such this often creates one of the more noticeable culture clashes. Westerners raised on believing that anything sexual is a "private" matter are often surprised to find how open the Japanese are, and often wonder if this means Japanese people are simply "weird" because of this. Really it's only "weird" to Westerners because of the difference in culture, to a Japanese person it'd most likely be weird to them to learn that Western culture has often shown shades of being kinda prudish (more in the past [there was even once a time you couldn't discuss pregnancy on TV because it implies "sexual acts" took place], but even nowadays this can still be the case, as seen with "moral guardians").