The only answer. Mark Hunt was getting smashed by welterweights, middleweights and even Sherdog's own Sean McCorkle! The fact he was able to go from that title contention is unheard of.
Have we ever found out what exactly was off with him? That kind of career low and then redemption only seems to happen with PED's, or if a fighter is dealing with some serious addiction or mental issue outside of the cage, or one just shows up to collect a check. I don't think Hunto's transformation was the result of PED's, so I tend to believe there were mental issues behind the scene.