One plausible theory is the slaughter in Jordan was the final straw for the fence-sitting Muslims who were helping to protect him.
Somebody squealed, Zarq's safehouse was exposed, and Zarq's minions took the easy way out. Either that or Zarq blew them up himself.
I hope this plausible theory is the actual reality.
It does seem plausible, and here's another variation on it--what if those same people were weary of the guy, as you say, and they blew him up along with his inner circle? Zarqawi never seemed the suicidal type, which is why I suggest this scenario.