Not sure its 'against' Rizzo - or against Bob Miller, the other in-house name that was mentioned before (although his handling of the Farm system this year has been blah at best).
Rizzo was quoted during the Drew negotiations as saying how pleased he was that Moorad (specifically) gave him more active involvement for some of the contract negotiations, and that this was an area that he hadn't gotten much experience in previously. He just may not have the kind of well-honed business background they want.
Plus, I agree - it is a good idea to go outside - God knows, we've griped at all the within-the-organization hires in recent years. If they really get someone smart, forward-thinking, and with good fiscal sense (rather than one of the oft-mentioned retreads) it could be OK. Someone outside the org will not have the sentimental attachment to guys like Gonzo, and may feel no pressure to try to make Voldemort's past contract blunders look good.