The difference is 100% the "instability" (whether it's actual or just perceived). But this rams home the idea of "the only thing we have to fear is fear itself."
If on-the-field results had ANYTHING to do with conference stability, the PAC would be hemorrhaging members after this season. IMO, the real issue is that fans, ADs, and UPs still have bruised egos from the defections. why that stigma didn't attach to the ACC after Maryland left? I do not know. I assume it's because no one gives a crap about maryland.