Now that is the interesting question. I can't imagine that the market for inferior CEO's is very large, although I suspect if the market began to shrink, someone would come along and argue that their jobs should be protected.
ALthough I forget the name of the jackass, one total incompetent was nicknamed "the Hatchet." The first company he brought to total ruin was Allegheny Ludlum. His efforts made the company profitable--but he fired/laid off people without much consideration for the company's viability after Year Five (his option realization year.)
He actually got hired a couple of times later.
Then there's the rummy who briefly ran Giddings & Lewis in Fond du Lac, WI. After a few years, the Board noticed that nothing was better--in fact, that many things were worse. So they checked around a bit--and found out that not only was he a complete idiot--but he ALSO lied about having a college degree.
It's an adage worth remembering that most founding CEO's are harmful to their companies after Year Ten; their entrepreneurial characteristics are fine early, but those same instincts are inalterably opposed to the structure necessary to build and maintain solid mid-sized organizations.