Plot hole: Towards the end of the movie we see Mr. Wilson peek out from his front porch, surprised to see Dennis biking back home with his wagon carrying Switchblade Sam, tied-up and partly unconscious. Either Dennis must have some hidden super-strength or knew how to tweak the laws of physics there is no way that an eight-year-old kid of his build could carry an adult of that size to his wagon let alone easily bike home with Switchblade Sam's weight. Plus being an experienced criminal like Switchblade Sam he may have offered some resistance in being caught doing so much less submit to a mere kid. (01:50:00)
Plot hole: During the bedroom scene, when Dennis shoves a flashlight into Mr. Wilson's mouth and nose, Wilson opens his eyes. It would be impossible for Dennis not to notice his open eyes, and realise he's faking being asleep, especially when he puts the light into Wilson's nose.
Answer: Because of what George said to him in the house after he was robbed. He hurt Dennis' feelings so he ran away.