He can but choses not to. It’s more frightening to be at a zombie like pace yet still finding your prey or getting there before them. Its a haunting inevitability to be plodding along no matter the pace of the prey. The killing blow by Laurie is done spontaneously but nothing is spontaneous about Micheal, with his plodding hair with frankensized clodhoppers. It’s more Zombie -like and mindless that way. As if killing Laurie is his only purpose. And Why? Maybe it’s family annihilation in full. Laurie is the sibling left he has to kill.
He actually can, during the Halloween Kills 6 climax, you can see him briefly jogging in the tunnel chase. Also when he stabs Laurie and she falls down the stairs in the first film, he dashes very quickly to the head of the stairs, also he runs and jumps on top of the car at the beginning of the first film, yes michael can run when it benefits him.
External evils are confronted physically and driven out of the town and away from the population and destroyed. Think of a classic Western genre film when the villain is forced to leave town or overcome by a group of people who rise to the occasion and destroy the threat away from the populus.