That was a 12 win, 6th ranked Louisville team he decided to stay at, compared to an Alabama with a losing record. My guess is coaching his little brother and it being his birthplace and Alma mater had a factor in him staying as well.
Purdue isn’t a terrible job, but you can’t ignore money.
as of 2017:
FOOTBALL REVENUE
1. Michigan $97,149,706
2. Ohio State $86,668,248
3. Penn State $75,527,152
4. Wisconsin $71,220,684
5. Michigan State $69,579,206
6. Nebraska $65,741,822
7. Iowa $52,498,092
8. Minnesota $49,188,752
9. Northwestern $36,212,907*
10. Indiana $35,520,657
11. Illinois $32,910,979
12. Maryland $30,071,434
13. Rutgers $28,657,722
14. Purdue $18,747,410
FOOTBALL EXPENSES
1. Ohio State $37,479,825
2. Michigan $36,597,583
3. Penn State $35,647,905
4. Michigan State $36,896,168
5. Iowa $31,137,043
6. Wisconsin $30,731,315
7. Nebraska $28,223,705
8. Minnesota $27,656,340
9. Rutgers $25,174,838
10. Northwestern $24,629,741*
11. Indiana $24,430,110
12. Maryland $20,779,161
13. Illinois $18,432,831
14. Purdue $16,951,809
So say he wins a B1G Championship, and Nick Saban retires. What happens when Alabama opens the checkbook for a yearly salary that is half of Purdue’s total revenue? There gets to be a point where you just can’t really compete with the blue bloods, and it’s a sad reality.