It's probably money, no?
I don't particularly see Manchester City as a big club still... But money talks. Because of what they've been able to do and establish, they probably bring in significant financial gain through multiple channels for the FA/Premier League and those funds will go a long way toward the football pyramid, grassroots development and of course, lining the pockets of the fattest of cats. It's to be seen how much short-term damage this would cause for the FA/PL if they were banished, but I do think it is a point that has to be made (assuming the allegations are correct which at this point it seems almost impossible they are not).
I've said this all along and it seems to be glossed over by the vast majority of media covering this story... Banishment, multi-tier relegation, stripping of honours won over the period in question are a must if the integrity of the game is to be protected. Manchester City have most likely earned all of this through cheating if the expected outcome is met. What's more, they have been able to develop their youth set up, stadium, and training facilities which is why I don't think just a relegation, even if multi-tier, is enough. Because they have been able to establish themselves in such a way that they would climb the pyramid again within a few years.
All this says to me is "You might as well cheat", because the trajectory you have gained is astronomical in such a short space of time that most possible punishments are only going to set you back a miniscule amount. Man City could realistically set up their own tournaments to play 'friendlies' against teams that are in their off-season or winter breaks who want match fitness. They can play their youth players in the Championship/League 1 to develop them, and loan out key players they want to retain when they're back in the Premier League. It's just such complicated situation and they will find ways around it, and come back up to the Premier League with money to spare by being in the green every season through legal loopholes. It just stinks.