The trouble is that the legs tend to be the bits moving the fastest.   Also, the police have to try to minimise the danger of hitting innocent bystanders.   The fewer shots they need to fire, to stop their man, the better.    Armed forces have different priorities, as a weight of fire is a tactical advantage in itself.   If the Taleban are keeping their heads down, to avoid the bullets, they can't shoot back and they can't see what the Royal Marines are up to.   Even so, when it comes to firearms practice, the soldiers and Marines must use the same priorities as the police, presumably.

Is it still the case that the FBI use pictures of John Dillinger for their target practice?