He was shot six times because that’s how many shots were required to stop him as he was charging the officer with intent to maim or kill (already demonstrated twice in prior 15 minutes). He should not have charged at all, but certainly should have stopped after being wounded 1... 2... 3... 4... 5, times, etc. The final shot to the head stopped him.
By firing six shots, the officer showed considerable restraint. The average number of shots fired by an officer in a police action shooting is about nine.
That’s how many bullets are in the magazine.