Same reason Mayo get a free pass alot of the time, most people dont want to hear or see them being portrayed as the bad guys. After the hoo-ha over blanket defence died down people just seemed to say 'ah sure its only Donegal and sure they didn't win any more All-Is'. Also I suppose it's charisma, he has something about him that people seem to really want to believe and follow.
And if JMG had gone on to be an agreeable person in media I'd say the same but IMO he hasn't, he is rubbing it in and milking it, and getting a free pass. Mickey Harte, despite his personal tragedies, and despite being basically a humble man throughout his long time in the spotlight, still didn't/hasnt get/got the free reign McG is given to enthrall the masses with his teachings.
Maybe that's because Jim and his followers are right and I'm wrong.