Zarqawi is AQ. He knows he won't EVER be a leader of anything other than his roving bands of terrorists.
He wants to be a kingmaker, not the king.
Back in Fallujah when he had a city and thousands of fighters and his own Shira council he did think he could be king, that changed after the second battle of Fallujah.
Our mistake with Sadr was never kicking him and the Madhi Army out of Sadr city for good.