Somebody on the ground couldn’t threaten your life with a concealed weapon?
Maybe they could but you have to deal with the fact that he’s complying. You told him to stop and he did, while it’s theoretically possible they still present a danger once they’re complying you’re kind of obligated to not shoot them, steer the order in a way to lessen the potential threat (”spread your arms away from your body, move over to the light, what the hell are you doing here”) and handle things peacefully. Back in the day the standard line was “stop or I’ll shoot”, nobody says the whole thing anymore but there’s still that implication, he stopped, you don’t shoot.