Because it's basically training everyone who watches it to get off on voyeurism instead of actually having sex. Watch too much and your dopamine receptors get fried to the point where you would rather have your girlfriend have sex with a nigger than actually doing it yourself (if you even bother to get a gf rather than just staying in your gooncave). I don't even think it's deliberate demoralization by DA JOOS, it just ruins the concept of relationships and is probably why so many zoomers aren't getting into them.
It's especially demoralizing when you go into JAV to get away from blacked garbage, only to find out that they're doing it too. And for some reason, it's only the smallest, most petite japs that are getting railed by niggers. The average under 30 Jap guy is a turbo cuck so it's not surprising, but this is not the way to fix the declining birth rate.