When I was a new Christian, I discovered a portrait of Jesus called the “Laughing Christ” at a Christian book store.
At the time I was attending a serious church, a church where the thought of Jesus laughing was most likely frowned on. Maybe Jesus smiled at babies and puppies, but telling jokes with his friends? God forbid.
Consequently, because the serious people at that serious church were so serious about their Christian faith, they presented Jesus as serious too. Serious equals somber and sober, which equals humorless and kinda mean.