The same thing that prevents the Executive Branch from ignoring their rulings.
If they are going to play Calvinball, Biden should take a page from Andrew Jackson ask them how they plan on enforcing any of that.
I think that would be terribly dangerous for Thomas' continued freedom, with all the light being shined upon the bribes he's taken. He's still a Federal Officer & beholden to those laws despite his recent mouth-noises to the contrary.