Because with Dirk and the Mavs, they were on a mission. You just knew after they won the Western conference championship, they would not stop until they won it all. Dirk posed with the Western conference championship trophy for one second and then bolted to the locker room and his teammates followed him.
With the Rangers, I get the feeling that they were just happy to be there again and prove that they weren't just a one-year wonder. It's gonna take the Rangers years of failure for them to get that hunger/motivation the Mavs had, which I have no doubt will come soon. The Rangers are still basking in their early success. Once they start feeling the pain of playoff exits, teammates being released/traded away, managers being fired, etc. then they will have reached that breaking point of learning how to finish.