Most Helpful Girl
He isn't really a man but as Dr. Loomis said "evil" he is just a being who is set on killing. He never speaks, runs and for awhile many people wondered if he ate anything. (He does supposedly eat dogs, rats etc) but thats never shown. He doesn't have to run because he always no matter what will catch up to the victim because they screw up. Notice how in the ones with his sister Lori he always walks slow and killing anyone who gets in the way? Its all a way to scare her. What is more creepy, walking with a knife or running? Walking means he isn't in it to get it over with but as a way to taunt. Its all a mind game.
Thats how I see it anyways. I have seen those movies many many times and always had my theories lol.
Most Helpful Guy
More often than not the villains (or "Slasher") in the slasher genre of horror movies don't run and don't need to run after their victims.
Michael Myers isn't the only one, even Jason Voorhees just walks as quickly as he could when in pursuit of his victims, with only exceptions in some of the very earlier prequels and sequels of Friday the 13ths and the Reboot version.
It's implied that they all somehow have and wield unnatural or supernatural capabilities and possibly could merely just "will" themselves and teleport themselves in proximity to their designated target before totally annihilating them. That is unless they are a pre-scripted and designated survivor of course.