Luck and his ability to ”cultivate” the press, at least according to Matthew Yglesias:
The good reputation he emerged with following his time commanding the 101st can be attributed in large part to the fact that conditions remained unusually good in his AOR compared to what was happening in adjacent AORs. But it was thanks to his good reputation from that first tour that he was selected to head up the vital ISF training mission during his second tour. That mission, however, didn’t go well at all. So why did Petraeus’ reputation stay good?
Well in part it happened because he’s a smart, articulate, well-educated general. But in large part it happened because he’s a smart, articulate, well-educated general who was (and is) very good at cultivating the press. In particular, before being appointed to command MNF-Iraq Petraeus was a source, both on and off the record, for a wide variety of journalists both those working “straight” reporting jobs and those doing more opiniated work critical of the Bush administration from both a moderate liberal perspective and a neocon perspective. During that period, he cultivated a lot of good will and credibility that he’s deployed to great effect since taking command. The fact that Petraeus has been a source for a lot of the journalists who cover the Iraq debate is a key element in understanding the politics of the surge and of the “Petraeus report.” But it’s a story that you’ll never see reported on in detail because that would violate the rules of the game.
Of course, that’s not the only explanation.