According to THIS SOURCE (the Arab-American Institute), Franks had been requesting that Abizaid be assigned as one of his deputies for many months, but Rummy kept on turning him down because Abizaid was in such high demand at the Pentagon.
I found this excerpt to be quite interesting:
"Still, there is little doubt that Gen Abizaid brings a reputation for high intelligence and quick decision-making that will be critical in a war where US troops are likely to be racing towards Baghdad - very unlike the standard slow-moving flanking actions used during the first Gulf war.
His reputation for decisive action was cemented during the 1983 US invasion of Grenada, where, facing a nest of hostile Cuban troops, Captain Abizaid ordered one of his officers to climb aboard a bulldozer, raise its shovel, and drive it towards the enemy while he and his men advanced behind it.
The incident became so celebrated that it was adopted by Clint Eastwood, who gave identical orders during his film about the Grenada invasion, Heartbreak Ridge."