Surprisingly, they did. Brett Gardner, Curtis Granderson, and Nick Swisher combined for 13.6 WAR in 2010, which means the Yankees actually wound up with the second or third best outfield in all of baseball.
Even better, the group is cost-controlled. The Yankees can keep the trio intact for 2011 and 2012 at a total cost of just $37.5 million plus whatever Brett Gardner makes in his pre-arbitration years (translation: nothing). Sure, GGBG's true skill level is probably somewhere below his 2010 numbers, but Swisher and Granderson are solid bets for 3-4 WAR each, so even with some regression that's still 10-11 WAR outfield for under $20 million a season. The going rate for 1 WAR on the free agent market is about $5 million, which makes both Swisher and Granderson good values and Gardner an absolute steal.
What could be better than getting above-average production from three players at below-market salaries? How about the fact that the only commitment to any of them beyond 2012 or their age-32 seasons are team options and arbitration?
If they perform well the next few seasons, they'll get paid accordingly, and if they don't, they won't. It's the ultimate win-win. Down the road, if any of them are still wearing pinstripes in, say, 2014 or 2015, they'll be paid based on where their skill levels sit then, in the middle of the decade, rather than where it sits today. There will be no albatross contract in this group's future, and that's a good thing from any team's standpoint.
So why would anybody want to mess with this by signing Carl Crawford?
Sure, he's superior player to those three, but the actual difference is probably smaller than you think. When you consider the current makeup of the Yankees outfield and who he'd be replacing, signing him is unlikely to net them more than a 1.5 - 2 WAR upgrade even under the best of circumstances. Despite this, Crawford is sure to earn almost twice as much as either Swisher or Granderson, and twenty times as much as Gardner, for no less than 5-6 years going forward. He's better, but not that much better.
His speed and defense are valuable skills that should age well, but let's not forget that he still has never slugged .500 or gotten on base above a .364 clip. He's a good player, not an elite one, and in a vacuum, the risks of signing somebody like this through his age-35 or age-36 season for close to $100 million probably outweigh the benefits. In the real world, where the Yankees already have a cost-controlled outfield that ranks among the best in the majors, it's utterly stupid.