Mark’s Down On Your Syntax said:

I seem to remember reading somewhere that the plan was to make the Halloween movies an anthology, but after the third one didn’t do much business they scrapped that idea and went back to Michael Myers (and apparently felt the need to remind people he was in it by including his name in every title!) It’s a shame really because Season of the Witch was fun and creepy.

Perhaps if they hadn’t made Halloween 2 a direct sequel to the first film, the idea would’ve had a greater chance for success.