no one wants to own the chaos.
and killing the debt ceiling after a breach is much, much worse than, say, also arguably illegal payment prioritization before a breach. it would invalidate lots of debt that will already be in (wealthy) private parties' hands.
existing US Treasury instruments go poof! is about the clearest path to calamity. Would an unpopular Supreme Court defending what the public perceives (if the admin plays this well) as extortionate brinksmanship really do that? /fin