There's probably more people who don't wash their hands after using the bathroom than people who pee in the shower.
I'd also imagine the vast majority of men stand when peeing (at home) when if you're worried about cleanliness of your home at least you should probably sit. I guess you can debate whether it's more hygienic personally to stand.
I don't pee in the shower and I don't get why people do it but whatever, it has zero effect on me outside of hotels I guess. So people can do whatever they want.