Cats are strange creatures and nothing’s stranger than cat behavior that can’t be explained. One of the more curious behaviors of cats is when their owners go to the bathroom and their cats follow.
Some people believe cats simply like the cool surfaces of porcelain, but then you’d expect cats to be in the bathroom all the time. Others suggest that cats know when you’re sitting on the toilet, you’re immobile so they can get all your attention. Still other people believe cats know you’re using the bathroom like a litter box but that doesn’t explain why they’d want to see you go to the bathroom either.
This mystery will likely never be solved because cats won’t tell us. So if you want to know the real answer, you may have to wait until you come back reincarnated as a cat.