This is what Dejan Kovacevic is saying on the PBC Blog. I've put the link here, although it's a pay site. This is the most-likely-to-be-accurate info we're going to get until they make the pick. It appears to boil down to the Pirates' concern over Rendon's shoulder--it's been reported elsewhere that doctors consider it "yellow," as opposed to "red" or "green"--and the fact that Cole has a much higher ceiling than Hultzen.