Because if they haven't they're missing a golden opportunity. Zobrist was made expendable earlier today when the Rays agreed to a 1-year deal with Asdrubal Cabrera, and Tampa is reportedly willing to move him. At age 33, Zobrist is a switch-hitting, multiple position-playing super everyday utility man. He's what Martin Prado would be if Martin Prado was better at baseball in every way and he's available on a steal of a 1-year/$7.5 million deal for 2015.
Simply put, Zobrist does everything well. He's a .264/.354/.429 career hitter, although he's posted averages of .270 or better in each of the last 3 seasons, with few strikeouts (15.7% career K rate) and a ton of walks (12.7% career BB rate). He's an above-average defensive player at second base and in the outfield corners, and he can fake it at third, shortstop, and in center in a pinch. He doesn't steal a ton of bases, but he's had 10 or more for 6 years in a row and he rates as an above-average baserunner.
His over-the-fence power has trended down over the last 2 years, but the high on-base numbers and good gap power make Zobrist a very useful and flexible offensive player. He's what we should realistically hope Rob Refsnyder becomes and he now seems very available if the Yankees aren't as gung ho about handing that job over to Refsnyder as they appear to be. This would be a step in the wrong direction on the "getting younger and creating opportunities for the farm system to contribute" front, but as Dom wisely put it in our email discussion, Zobrist instead of Refsnyder "is the exact kind of player they need to be going after to play the 'we're rebuilding but are still semi-contending' card."
Obviously Zobrist is not the type of player you sell the farm for, and the Yankees are going to balk at any kind of deal that asks for too much of their top prospect talent. But the Rays haven't exactly been fleecing teams on their other trades this offseason and aren't in a position to ask for too much with the deal being for but 1 season of Zobrist's services. While it would delay the introduction of the kids at second, adding a 5-WAR player to the lineup and replacing the lost Prado flexibility would be more than worth the 1-year delay.