Ashley lives for failure. Any time things are going well he kills it off. Keegan returns and creates a feel good factor, getting the team winning again - Forced out. Hughton picks the team after they've been embarrassingly relegated and wins promotion emphatically - sacked. The team finishes 5th - He invests next to nothing in the team in the summer and then actively begins asset stripping the team.
On the other hand Pardew stinks up the club for nearly 2 years doing what seems like irreversible damage now and never gets close to the sack. Just so fucking hopeless.