Because if Mesa files for bankruptcy while the MOU is active, then a bankruptcy judge can say, "okay, the floor is 0 hours and the ceiling is your MOU. Start re-negotiating before I do it for you."

This is how airline bankruptcies have played out in the past. Don't expect signs of a bankruptcy filing before a filing happens... just like you don't expect a heads up about furloughs before news about furloughs breaks.