Bill James gives us a peek behind the curtain:

About 2004, when the Red Sox were in the market for a shortstop, we tried to trade for Adrian Beltre, with the idea of moving him to short. I’m certain, having watched him play third, that he could do it. But you have to overcome that resistance, of “this guy doesn’t LOOK like a shortstop,” and it’s really hard to do that, because organizations tend to make decisions by consensus, and the consensus is always going to rely heavily on images.