It was a numbers game decision in sending an outfielder in Robinson to Baltimore for an infielder. Robinson would have had too much competition in the outfield to get playing time while Andino provides the Mariners with depth in the infield. Andino can play both middle infield positions and started at second base a lot while in Baltimore due to injuries to Brian Roberts at that spot.
Andino, 28, isn't the strongest of hitters with a .235 career average but he's still better than Robinson has been over 90 games with the Mariners. Robinson, 25, hit .215 with five home runs and 26 RBIs while with Seattle.
Trading a young prospect for a veteran is a trend started last year when the Mariners dealt Josh Lueke for John Jaso.