This is an excellent point. It may be a matter of working through definitions. Are there multiple social contracts that happen at a game table? For instance, is there one social contract in the form of the "rules" of the game's universe/society and another social contract in the form of the relationship between PCs both in and out of character? Should we perhaps consider the relationship between the PCs as a type of meta-social contract? And does this meta- position allow the players to simultaneous critique the social contract of the game's universe/society and the social contract of the player's own society?
These are types of questions I'm interested in when it comes to critical game theory.
I think there have to be multiple contracts. The characters need to act in a manner coherent to the game world (not the setting, but the actual 'play' world - time travelers/dimension hoppers don't have to act according to the period/place they travel to, but according to the world they travel from etc.) and agree to have a shared foundation from that setting. The players need to act in a manner that allows everyone to enjoy the game (not being a spotlight hog, minding the table talk etc.) and collaborate. The GM needs to respect the autonomy of the players and make them an active participant of the story and not just narrate their own vision.
I also think one further contract should be in place - that everyone needs to agree and act in accordance with the style of play they set out to achieve. If the players agree to have a cooperative game, then even a rebellious character should be rebellious only to those outside of the player group. I feel that there should be a give and take in a good game, and that when people act solely for their own perceived reward, they can actually make everyone, including them self, have a poor experience. I see it somewhat like the Harm Principle, in that your right to liberty is tempered by its impact on my right to liberty. I like gaming for a net-positive result, whereas I see many people acting for a net-zero result.
I just don't think it is fun unless we all play the same game at the table.