Not sure if this has been mentioned yet, but I think the massive salaries that even Iowa State-type schools can now afford has changed the game for retaining good coaches (thanks to TV contracts with unpaid student athlete labor).
Unless you are after status, the added stress and expectations of a blue blood aren't really worth bumping your salary from $3M to $6M. At some point there are diminishing returns for overall happiness if you already have more money than you need.
Let's also not discount the job security side of this. Some coaches may be able to bump from $3M to $5M or so by jumping to a blue blood, but you may also lose your job within 18 months (hello FSU). The job security at a place like ISU is much higher than most jobs, so getting $4M per year here vs. $5.5M at an FSU, USC, etc could be MUCH more valuable long term - not only in comfort, etc, but also in $$.