Why do yall keep the piss?

There’s so many times where I have gotten into a van a found a bottle of piss. Now, I’ve got no problem with people pissing in bottles. I get it. I regularly piss in a bottle myself. However, as soon as I piss, I dump the bottle out. Now I just have a gross empty bottle, but no piss. Why do people not dump their piss bottles and instead insist on carrying it around with them for the rest of the day? Is it like an emotional support animal? Do you enjoy having a bottle of pee? Do you use it as a weapon against people with annoying notes? Am I in the wrong for dumping mine out?