Also - and I’m only familiar with the 1971 film version with Gene Wilder - Grandpa Joe is clearly the only friend, companion, and available adult in Charlie’s life who he can talk to. His mother is too busy from working to support the family. He doesn’t have friends or money to spend. And Grandpa Joe does show some guilt and awareness about not contributing more to the family. He has that great line when Charlie tries to give him a nickel for tobacco: “When a loaf of bread looks like a banquet, I’ve no right buying tobacco.”