“Over night” is certainly less than 4 years, regardless of exceptions. And no coach has gotten less than 4 years (outside Sampson for obvious reasons). And the ones that showed flashes of elite potential, got more than 4 years.
I do think you’re right, that when IUs base turns on a coach it’s over. I just don’t think that’s unique to IU. And there’s zero reason to hang on to coaches, regardless of the mood of the fan base, when it’s clear your current coach isn’t capable of getting IU back to where IU has been in the past.