How did these miserably failing CEO's manage to stick around for so long (often to the bitter, painful end) of their failing companies?

Robert Palmer at Digital Equipment Corporation (DEC)
Eckard Pfeiffer at Compaq
Carly Fiorina at HP
George Bell and Patti Hart at @Home
Jonathan Schwartz at Sun
George Shaheen at WebVan
John Sculley through Gil Amelio at Apple
Bernard Ebbers at WorldCom
Kay Whitmore at Kodak
John Rigas at Adelphia (so badly messed with the company's money that he ended up in jail)
Kenneth Lay at Enron (similarly would have gone to jail if he hadn't died first)

Now that I'm looking at such a long, long list.. maybe this isn't as rare as one might have hoped. Hmm?
Don't worry for Elop, though. I'm sure he'll do just fine even if Nokia dies off.