why would you be committed just because the nose wheel is on the ground?
Because at that point, being a good pilot who keeps his nose wheel off as long as possible, it takes less distance to stop than it does to get airborne again
If you have to reject the landing due to an obstruction then at that point you're going to hit it if you try and get airborne again.
From an ATC point of view also, I wouldn't dream of sending an aircraft around from the "nose wheel on" position if I judged the speed slow enough to make acceleration and take-off unsafe - and if the aircraft has been landed properly then that is the more likely possibility.