My head cannon is that there’s no such thing as a pee fetish, and the entire idea is propped up by the overwhelming sales of synthetic piss from sex shops in order to pass drug tests. Some porn studio marketing team noticed the sales and decided they should fill that niche, but all the viewers are just confused people watching out of shock value.

Basically the war on drugs inadvertently created a massive market where people piss and shit on eachother and think they like it.