The 2-3 zone was designed to make you rely on the outside shot. But as teams moved toward building their offenses around the 3 point shot, this once well-designed defense became a liability. Boeheim's apparent refusal to evolve gradually led Syracuse to mediocrity.
That's not to discredit his entire career, but the game passed him by. He's not the first and won't be the last, but it seems apparent that his "retirement" wasn't really his decision. More of a concession to a coach who gave a lot to the university, but whose time had passed.