It's a hypothetical joke. It is axiomatic that it is funny, that's established in the premise... there is no 'why'.

If someone wants to try to argue that objectively funny joke isn't funny because of the reader's anxiety that they may accidentality be laughing at something made by AI then they're welcome to try.

Keep in mind that the meme isn't 'It IS AI so it isnt' funny' the meme is 'It is funny but I can't laugh because AI exists'.