was it ever explained what in the hell Michael's motives are?
H1- just Evil, no other explanation needed.
H2 - We find out Laurie is Myers sister and he wants to kill her, still the same night as the first film
H3- No Myers, Completely separate story. The first Halloween movie cameos on a TV during the film.
H4- Laurie died in a car crash and now Michael wants to kill her daughter and his niece. 10 years after Halloween 2.
H5- Still going after Jamie and now sports a thorn tattoo that isn't ever explained a man in black follows him through the film and breaks him out of jail at the end of the movie.
H6- Finally manages to kill Jamie and turns out she just had a kid which Myers tries to kill. He's secretly being controlled by the man in black whose the leader of the town's cult and which is why Michael had a thorn tattoo in the last film.
H20 - Continuity REBOOT, only Halloween 2 is now canon. Still trying to kill Laurie and gets his head chopped off at the end of the film.
Halloween Resurrection - Myers secretly disguised a paramedic as himself and slashed his throat so Laurie killed an impostor. (Gotta keep the sequels churning out) He kills Laurie in jail at the start of the film because Jamie Lee Curtis is sick of this franchise at this point. Myers spends the rest of the film murdering stupid teens filming a reality show at his old home.
RZHalloween -REBOOT again - Michael is raised by his redneck abusive family and is obsessed with Laurie still his sister. Gets shot by her at the end of the film or something else depending on the home media version.
RZHalloween 2- Michael still alive and stalking Laurie. He now looks like a hobo and chases her throughout the movie and sees visions of his ghost mom because reasons? Gets killed with Laurie by the Police in a shed at the end of the movie. There's another ending from either the unrated or theatrical. I can't remember which is which.
Halloween 2018 - Continuity REBOOT - Only Halloween 1 is canon now. Laurie is still traumatized years later while Myers was caught and sent to jail at the end of the first film. No longer her brother in this continuity he breaks out and runs into Laurie again due to the doctor that took care of him after Loomis died.
Now you should be all caught up on the convoluted multiverse timeline of Halloween series.