Well, besides getting Charlie to steal a drink in the factory. this guy had been laying in bed with the other three grandparents while Charlie's mom worked her fingers to the bone to take care of them all. And the second something fun comes up, dude is singing and dancing. I mean, I realize musical logic is a thing. But he didn't need any help getting around after that. He clearly could and just instead decided to let his daughter or daughter in law just... take care of the whole family without help.