Because a lot of Yankee fans are idiots. That's why. I love my Yankees, don't get me wrong, but I don't love all Yankee fans. Every move has to be looked at as a "What can you do for me now" kind of move instead of a "f*** you, you were a Red Sox player, AARGH!". There is tremendous upside to this move.
Another interesting development is brewing. Sounds like the Yankees are close to a 2 yr deal with Ichiro for around $12 mil total ($6 mil AAV). That, to me spells out two things.
1. The Yankees want Ichiro to be in range of 3,000 hits in a Yankee uni (he needs 397).
2. Granderson is gone after 2013.
#2 is more because the Yankees will be able to produce one OFer for 2014, barring a catastrophe, as I have actually left out a few candidates previously. Ramon Flores, Zoilo Almonte, Abraham Almonte, Slade Heathcott, Mason Williams, and Tyler Austin should all be a AA or higher in 2013. One of them should make an impact enough to start the yr in the bigs in 2014. And as my avatar suggests, I think that'll be Tyler Austin. Sounds likely that Gardner is the CFer, Grandy the LFer, and Ichiro the RFer for 2013