Because this isn't actually a Micheal Myers movie. It's a Halloween movie.

Which is to say that this borrows heavily in spirit from Halloween 3. Infact, this set of 3 movies are all spiritual sequels to their counterparts in the original 3

1: Both have Myers break out of custody and wreak havok on the town and barely survive an uncounted with Laurie.

2: Set immediately after the first one, Laurie is take out of action for a large chunk of the movie, higher death count, Micheal actually gets in fights with the cast rather than just straight up murders.

3: Not a Micheal Myers story but rather part of an anthology. Similar opening blue title card with the same font.

But in the end, they know they need to actually finish Micheal's story, so it is tacked on at the end.

I'm not saying it's right, but they clearly made this movie (and trilogy) with the intentions of echoing the first one, which means that 3 needs to be atleast an attempt to look at another story that takes place on Halloween.