Michael's Curse

Many people have asked "WHY DOES MICHAEL KILLS HIS FAMILY ?"

Well in HALLOWEEN 6 Tommy doyle reveals Michael's secret:

When Michael was a boy, he heard voices yust like Danny in H6. The voices wanted that Michael started to kill all his family members. Because Michael has been cursed with the Thorn(that thing on his hand in H6), where a young man must wipe out his entire family for the good of civilization. So thats why Michael Myers killed his sister and his niece.