It's likely not easy finding an experienced coach that wants to come to a bad team. And unless you have a proven pedigree, you're going to be asked to take the reigns on one of the leftover teams.
Johnson and Frank have done so, and I'm not sure that it worked out for them all that well. I would say the biggest thing holding Sam back is that he doesn't have a work ethic that can match a guy like Casey, and you really need that. He's got too much other shit on the go and is likely happy not coaching unless he gets a plum job.