You mean they weren't already?Nowhere Man said:They would just get too exhausting to watch.
Substantively, while I don't mind a more serious tone overall, you can't do 100% super serious all the time. It just gets boring. You need smaller, lighter, even funny moments from time to time just to make a story work. It's all a question of timing. When, how, and how often you drop a joke matters more than whether or not a joke is there.