Because you don’t like the smell? You’re afraid other people will think you are gross? You have been trained to fear pee?
In normal circumstances getting urine on skin (or drinking small amounts of it for that matter) is not going to cause you any health problem. Urine contains various toxins your liver removed from your bloodstream, so drinking large amounts of it might not be the best idea.
Modern American (and possibly other) cultures have various taboos around cleanliness, including disgust about pee and peeing. But often these are not based on serious health fears.
Actually, if you are just using the bathroom to pee, you should probably wash your hands before you go, as your hands are usually "dirtier" than your genitals are.
Because you just touched your pelvic region which has tons more bacteria than urine itself does. Urine will have some, especially some from the urethra on the way out, so definitely shouldn't be considered sterile, but wash your hands if you're touching your pelvic region in general please.