Was it really so much of "Communism won" rather than collectivism reared its ugly ass head again? From wht I've read on Sols they have a large chunk of "Human Supremacy" dogma, which is ultimately bad for societies. Sure, it may last for a bit, but eventually it would collapse under the weight of its own prejudices.
IMTU, The sols lost control of Earth because they couldn't stand up to the Imperium, which makes a lot of sense because the Imperium had been at the whole interstellar brinksmanship game for a LOT longer period of time. I also changed it to where the Sols almost lost internal control due to incredibly powerful megacorporations (complete with Private Armies/Fleet), but they won in the end after a series of brutal and destructive "Corporate Wars". At the moment of 1100 imtu, there is a James Bond style cold war, spanning several Sectors between Sol and Imperial space.
Two things I never liked about the OTU were the "Sols can do anything!" sort of attitude and the "Stagnant Imperium" attitude. Imho, any empire spanning so many sectors (sol or imp) would NEVER be socially stagnant.