"Single sign on" means "contact centralised provider with identifying information plus site browsed".
The explicit desire here is to stop that tracking.
Tracking _is_ single sign on with the "sign on" being invisible to the user.
(Mind you, Google themselves are working to move enterprises away from this model, with their https://cloud.google.com/beyondcorp/ effort avoiding the "Intranet as a bunch of services on separate internal domains" model, in favor of a "Intranet as a bunch of services all living under smart proxies that make them look like one domain and handle IAM for you" model. But enterprises would need to move first, before complete tab isolation could be workable for them.)
There's also even-more-enterprise SSO, i.e. SAML and its "using your bank as an SSO provider to prove your identity to government services" use-cases. This actually isn't SSO at all—there are more identity providers than there are services. The point here is to federate proofs-of-identity by allowing many different (whitelisted) agencies to vouch for your identity, so that the government doesn't need to issue you some centralized proof-of-identity. This would also break under complete tab isolation, and I don't think there's any good replacement in this case.
(personally I get a small hit of joy every time I hit a site that is caught and blocked trying to do things it shouldn't, and vow never to return. it's better than it happening without knowing.)
If you don't want every tab to be connected, every tab isn't connected.
It's not like the problem is impossible; nobody is saying that. My point is that the solution is non-obvious to the point that nobody has solved it yet, despite likely man-years being put into trying. Firefox Containers are the best UX we've come up with so far to kinda-sorta solve the problem. Do you have any better idea?
