Why voiding and ejaculation NOT happen simultaneously? -
there-s a valve, sorta like a swing gate, between the bladder tube and vas desi(something) that makes sure that doesn-t happen.
Essentially, guys have a sort of valve that only allows one channel to be open at a time. Sexual arousal takes precedence, so while the guy has an erection, he can-t urinate. Howerver, it-s apparantly possible for some guys to ejaculate while they-re urinating, or so they claim.
Why would you want to pee and shoot at the same time?!
To answer your ?, different valves.