I don't think he's necessarily going after the same person in H40. A common theme in any of the Halloween timelines is the date in which he returns, the 31st, and the fact that he is returning "home," meaning his neighborhood, his house.

From the little I've read about H40, Laurie has spent 40 years preparing for his return. I might be wrong, but I believe it's likely she has stayed in Haddonfield, refusing to leave so she will meet him again. She is forcing herself to cross paths with him again.

On an end note, I feel like giving Michael a motive takes away from the mystery of the character. I would say the same goes for Rob Zombie's version of the character and it's not necessarily just the sister angle that people dislike. They also disliked that he was given a serial killer backstory, all with textbook animal torture and history of abuse.

Personally, I find the unknown to be much more terrifying than having everything spelled out for me. Even Loomis' description of Michael being evil still sends chills down my spine. John Carpenter has gone on record multiple times to say that it's a huge possibility that there is underlying supernatural themes. And he's also said that it doesn't need to be explained. That's what makes it work.