Because Phil Fulmer is NOT Johnny Majors. Heck ISU is not Pitt...it could turn out worse than your example.
They both spent 15 years at Tennessee, with similar success.
At 57 years of age, Johnny Majors went to take over a struggling Pitt program (which he has great ties to and motivation and incentive to win at) after a season nearly identical to what Fulmer just went through.
And he did nothing. He left them after going 4-7 in 96. Pitt hired Walt Harris who came in and went 52-44.
The point is that just because he's a "name" who has had great success doesn't mean he's going to be a great coach at ISU, and that doesn't put him any higher on my list than any of the other guys we've been talking about.
Johnny Majors to Pitt in 1992 is almost IDENTICAL to Phil Fulmer to ISU today. Doesn't mean it will turn out the same, just that it very well could.
Then again, Walt Harris (after a couple of bumpy "rebuilding" years) went to 5 straight bowl games, and had 1 9 win, 2 8 win and 2 7 win seasons over that timeframe (even though they lost to ISU in one of them!). Then, he went to Stanford where he promptly was fired after 2 years and a 6-17 record.