Because they said they were gonna get under the 189 million threshold, of course!
Seriously, there were a lot of stories about the Yankees being determined to get under the 189. In retrospect it seems laughable. However, there were two factors that lent the story some credibility:
1) Supposedly, there is a big, bad new financial penalty for luxury tax payers in 2014 - the 'revenue-sharing-disqualification' penalty, or words to that effect, which some stories projected could be in the tens of millions for 2014, on top of the 50% tax.
2) The Yankees did seem to be trimming payroll a bit the last few years, most notably last offseason when they cut Swisher and Martin loose and made no effort to replace them.
The current spending spree does raise the question of why the f*** they let go of their best hitter by far.