You realize the majority of people who get perma banned, which is a huge number btw, get banned for griefing or stealing, with irrefutable evidence (logs).
This would be great if this server was still really under an rp category for play trials. But for real punishments it's a waste of time, effort, and would be a mess to organize for the sake of someone who will probably go off and steal some more blocks later or during the trial, be a troll the whole time. All the while the ban appeal takes little to no time or effort beyond checking logs and communication between mods.
The Jury, even if selected from online players, wouldnt want to stop what they're doing for a griefer. I wouldnt, I'd probably log off and grab some lunch before wasting my time.
The Lawyers, mods, admin, ect.... Have better things to do with their time and other obligations no one wants to have them put on hold
The Judge, sawine or admin, Most definitely has better things to do.
Hell, every player has better things to do, even if it were volunteer based, we may have one or two people willing to do (some) of the positions and they'd probably be either unqualified to make a decision or they'd just be a troll or, frankly, stupid.