I've had mechanical throttles get stuck, too. But it wasn't an issue as I would hook my foot under the pedal and pull it up, or just turn the key off. Or push in the clutch. Or shift to neutral. Or step hard on the brake (the brake is stronger than the engine). My car also has a separate switch for the fuel pump, which can be turned off.

The point is there being multiple independent ways to stop the car. Running everything through the same central computer makes for a completely unsafe system.