Seems like your biggest hang up is the word ‘contract’, which you have assigned a lot of concrete properties to. Would it be easier to understand if they used the word agreement, and described it in softer terms like the general agreement everyone in the world has that punching someone in the face is not an acceptable for of greeting? I mean, no one has said that, and you haven’t personally gone up to everyone and stated this and shook hands on it, but it’s still something everyone agrees on.

The social ‘contract’ is like that, it just uses an unnecessarily official sounding term in it, but ultimately is just the understanding that some concessions have to be made to deal with other humans. The terms of the contract are really to vague to ‘sign’, and when people start referring to more specific terms things can go of the rails pretty quickly, but there is still an implicit agreement. It’s like living in an apartment where you didn’t sign the lease…sure you’re not legally bound by the terms in the same way that someone who did sign the lease is, but your still bound by them in some ways simply by living in the apartment. In the same way, continuing to live in society is the way the ‘contract’ gets signed.