Actually, the way I'd like to see it is this....
Crime goes up. Troop loss from all in the fief owner's faction goes up. No real reason to hit the traders, but if it must stay, it stays.
As each soldier leaves the army, population increases. Free troops on the defense right? Not quite. If Crime is 0, normal population exists. If crime goes up, the fief owner, and their faction pay the highest penalty, and the population increases as the deserters rise. If the population hits 'x' amount of people, there's a rebellion. AI fief against the troops that are STATIONED in the fief, with reinforcements not possible. This forces a faction to keep troops in the garrisson to defend it, as well as gear.
It makes sense. The deserters want to rule... the population is unhappy with the crime rates... the faction and owner are penalized the most for not managing the fief properly... and it opens the doors for new owners, and new factions to take gain territory.
The rebellion isn't a guaranteed 'win'... the AI still needs people to fight for it.
Just my thoughts.