Because that isn't what the law says, and the man is an obvious crackpot.
Because that isn't what the law says...
Beyond that, you have provided a possible answer to the question of jurisdiction yourself in less than ten words. The judge couldn't have ruled in such a way himself?
If it's obvious he is a crackpot, then why bother with the process of testing his mental capacity in a formal way? If the man's argument had no merit, the judge could have warned him not to waste the court's time, and that other such "crackpot" behavior in his court would be answered with a charge of contempt.