Umpires got power, man. You ever notice if you go to a ballpark and there's a close play on first base, they will not run the replay at the ballpark? I've seen umpires go underneath and call up and say if you run one more of those replays, we're gonna forfeit the game. That's how strong their union is.
Justified or not, the Supreme Court has a kind of sacred status in American life. For whatever reason, Presidents can safely run against Congress, and vice versa, but I think there is an inherent popular aversion to assaults on the court itself. Perhaps it has to do with an instinctive belief that life needs umpires.