It’s possible that he’s already been killed or tortured to such an extent that releasing him would raise more scrutiny than disregarding the judiciary. Considering the naked sadism motivating this, I suspect they’re keeping him alive as a hostage. If the Supreme Court actually orders the regime to do something it doesn’t want to (unlikely; they’ll find a face-saving way to submit), I think they’ll want to pointedly show that Abrego Garcia is alive to send a message when he “commits suicide after privately confessing guilt to El Salvadoran authorities”. Trump and Bukele will laugh about it on camera and say they did their best to comply, but there’s nothing they can do now.