I think that behind the scenes, somebody told the 5th to shit or get off the pot, and that SCOTUS just went out on a limb for them to preserve circuit court autonomy, which per Kagan’s dissent, they are currently abusing. The Appeals court was pretty clearly slow playing this in a partisan manner.
I think it’s important that we remember that at SCOTUS, even most of the conservative Justices (seriously… fuck Clarence Thomas, even apart from RV corruption, he’s been a joke of a jurist for decades) still want to believe they’re on the right side of precedent and history, so we can often suss out their reasoning, even if it’s deeply flawed and disturbing.