According to Osho, laughter is natural, but we’ve been made unnatural by ego and social conditioning—morality, ambition, and fear of our own nature. To stay in control, we repress spontaneity, becoming sad and rigid, so even jokes can’t touch us. Drop pretensions, relax into ordinariness, trust nature over ego; then laughter returns spontaneously.
You can’t laugh because you’re pretending and controlling; be simple and real, and laughter will happen by itself.