it's not about the punchline, it's about the fact that jokes are an extremely complicated thing. The reason? It's a highly abstract structure of information, not unlike low-level speech (how words are supposed to be put together in different languages), code (different programming languages have different rules for commands and sequences).

Even the best LLm's are still at the level of children in this abstraction, so they can't make "quality" jokes. They also suffer from not having a unique personality and being the average of everything. Until this is addressed, don't expect great jokes to come out of AI. It's almost the most challenging discipline. I wouldn't be afraid to make the comparison that the "joke" is the real Turing test.