This is probably a bit of a stream of consciousness but here goes ..
I don't think Moyes is "stealing a living". I think it's more to do with him being a very 'old school' manager who hasn't actually adapted to the modern game. If you look at what he did with Everton, you can't deny he did a good job with them on a restricted budget but the thing is, he had time - and a lot of it.
A manager like that probably can turn a side around and into a decent footballing side if they get the chance to work with the players over an extended period, but I guess the problem he had, and has, is that he's now in a situation where he needs to turn teams around quickly and start getting results quickly otherwise he's immediately under pressure.
Someone like Steve Bruce, Allardyce even, probably has a way of working that he knows will get the players going in a short amount of time, and it's proven to work - that's largely why he's never out of a job.
If Moyes went to a club like, say, Blackburn where the fans would probably just be happy with a bit of stability and staying in the Championship in the short term, then he'd be out of the spotlight for a while with no pressure and probably would get the time he needs to actually do a job for them.