I think it's actually case law, not statutory law - and not pertaining to coaches, but rather contracts. The idea is that one Governor cannot handcuff the next Governor as far as contracting is concerned. The 2nd Governor has the ability to cancel any of them and re-bid them, which is why the custom has become a 4 year contract, which would be concurrent to a gubernatorial term.

Don't ask me a bunch of questions beyond that, as it's all I know.