A judges whole job is to interpret the law and to apply appropriate penalties given the circumstances.
In some cases crimes have prescribed penalties - “exceeding the speed limit by 5mph” probably has a prescribed penalty.
In other cases the judge must weight the circumstances and determine what penalty is appropriate.
In this case, trump is antagonising the judge because it keeps his base engaged, and keeps campaign donations flowing in. Trump wants to go to jail because it would ignite his base. Why would a judge feel that penalty is appropriate? May as well give him a blow job.
More to the point, the primary objective of any punishment in this case would be to cause Trump to desist. If putting him in jail is not going to do that, but rather give his contemptuous remarks a far greater reach, then why indeed put him in jail?
Honestly, the best course of action for the judge and the correct “punishment” for Trump is to give his various utterances the least oxygen possible while preserving the authority of the court.