Revealing mistake: When Jen is decapitated, its blatantly obvious its a fake body.
Revealing mistake: When Jen has her head cut off, the cord to the camera would be severed too, yet it is still broadcasting when her decapitated head is lying at the bottom of the stairs.
Revealing mistake: When you see Freddy's car parked outside the Myers' house when the trunk is open,you can easily tell that the background is artificially created and there is a wall at the side with painted clouds. (00:27:20)
Revealing mistake: After the hallway camera cuts out, it eventually comes back on the computer screen that Deckard is looking at. If you look at the landing and the stairway, the picture is reversed. (00:40:05)
Revealing mistake: When Dr Mixter is talking about Carl Jung in the classroom the camera pans over the students and if you look at the blonde girl with the pink sweater on she stares at the camera for about a second. (00:16:35)
Revealing mistake: At the start after the main title appears you can see the outside of Haddonfield University and you can easily tell that the building is a digital composition. (00:16:10)
Revealing mistake: When Michael is hung from the window, an upwards shot reveals the top of the sound stage the Myers house was built in (top right corner). (01:13:42)
Revealing mistake: In the H20 flashback when Laurie cuts the head there is no blood from it.
Revealing mistake: When Deckard and his friend are in his bedroom on the computer you see a window beside him and outside you can see that there are painted clouds on a wall. (00:20:20)
Revealing mistake: Freddy's car is parked outside Michael Myers' house twice. First, when the trunk is open with the adapted machine and then he parks on the other side of the road after Charlie gets killed. (00:27:15 - 00:30:00)
Revealing mistake: At the end of the film the garage is on fire and just before Freddy bursts through the door, there is a really quick close up shot of Deckard kicking down the door. (01:16:30)
Answer: Or maybe he's thinking that his mission to kill Laurie is done. He's been trying to kill her for a long time and succeeded. No need to continue, but when those kids invaded his house, the killing began again. No one goes into his house, but him.