All of those subpoena cases are working their way through the courts. (Trump keeps on losing.) Some may be decided very soon at the Supreme Court. John Roberts legacy depends on it. And he has to be on the court for many years. Trump will be gone sooner or later. Why give up your legitimacy for somebody who is almost out of office? Trump has no loyalty to anybody: Why be loyal to him? You would ruin your reputation when the next Democratic administration sends him to prison.

All they have to do is refuse to hear the appeals at this point, which should be easy since there are no legal questions at issue.