It varies for different posters, but I think it boils down to rationalization, blind faith, and fear of change -- or some combination thereof.
For some, expectations have also shifted to where a 12, 13, or 14+ loss season is "acceptable" so long as we make a sweet 16, which then offsets the generally subpar rest of the season in their view.
The bottom line is that the slippage is palpable, and it represents a steady decline. And in order to reverse that decline, we're going to need a fresh approach, and an infusion of new ideas / energy.
Though I agree the decline is not new, this is the first year I've felt strongly that it's time to change things. There are two main reasons for the hesitation before this. First, for a while, that '09-14 run was not that long in the past. Now, suddenly, it's eight years ago. And there was a period there where I think it was reasonable to think the recruiting problems were driven by the NCAA problems; at this point, I don't think that is plausible any more.
Second, the flip side of moving on is that it comes with an awful lot of risk, and I think people tend to underestimate how long it can take to recover. Five years after Dean Smith retired, UNC was on their second coach and went 8-20. And the cupboard was a lot less bare at UNC. Five years after John Thompson left Georgetown, Georgetown went 13-15. Even look at Arizona, which found a strong replacement relatively quickly in Sean Miller, had three coaches in three years after Lute Olson.
Additionally, even the home-run hire is not going to replicate the literally unprecedented consistency Boeheim put together for the first 40-odd years of his career.