So says Buster Olney at ESPN.com:
Four years ago, Mark Prior had the kind of stature that Johan Santana has now, as the pitcher that everybody would love to have. But now the Chicago Cubs have made it known that they are willing to trade the former All-Star pitcher, rival executives say.
For value received, sure, I'd trade him, rather than just let him go. But now that these "rival executives" know that the Cubs are offering him, why would they deal for him now when they can put the pressure on the Cubs by making them wait past the non-tender deadline?