It’s not even the least bit surprising.

Humor rests in large part on communicating some relatively easily understood idea in an unexpected way. It’s setting off on a statement or a story that seems like it’ll end up at some predictable and humdrum place, then suddenly veering over to some unexpected place that reveals some hidden insight.

And that’s something that LLMs just can’t do. By design, if they start heading in one direction, they will and can only continue in the most statistically probable way. And statistically probable is the one thing that humor very definitely is not.