Because he seems happy and has at least been quoted as saying he would be down with returning next season even if he got traded. No reason not to stay with what you know if you're happy and the money is the same. I think Girardi has already proven this theory wrong, with the same two teams involved. Unless maybe he's super happy about managing the team on the selling end of this deal. To put it another way, which team's future would you take, which manager would you rather play for, and which bunch of guys would you rather hang with for the next half decade? I'm guessing Chapman sees it the same way as JHey did and he signs up eventually. I mean, it's not like the Yankees don't have the resources to get back into contention rather quickly. It's not a stretch that somebody, if cool with playing for the Yanks right now, would view that situation just as good and wouldn't feel the need to move without a raise.