[Jack of Arcades]

Second base is a pretty physically demanding position. Moving the highest paid player in baseball there would be nuts. They've got the second shortest lifespan of any position player behind catcher. Tons of 2nd basemen just die off after they turn 33 (see Roberto Alomar).

Plus he's got a good arm and it takes a while to get used to the throws, etc. Third base is a lot more seamless, and many shortstops make that transition if they have the arm to.