there is the potential for high replacement cost to changing coaches. such that you could replace a coach with a coach of exactly equal capabilities, but damage your competitive position through foregone recruiting opportunities, lost recruits & transfers. since there is no shortage of qualified coaches, that's one big driver of coaching salary increases. the other being the substantial risk, and very high cost, of making an unsuccessful hire.
the other side of the coin is that there is some tradeoff between annual salary/perceived loyalty and job security for a coach. as long as a program is successful, the tradeoff can be masked. however, a couple of down years bring it to the forefront.