Why Britain kept treaty restraints after Japan withdrew

Did anyone continue to care about the treaty after Japan withdrew?

Yes. Britain and other powers kept many restraints in the hope Japan would return, a policy that failed and left them reacting late.

Treaty compliance retained diplomatic value even after Japan stepped away, because the remaining powers wanted to keep a route back into the framework open. That hope failed, and the delay left compliant navies adjusting hurriedly when conflict made the old limits untenable.