The reason has nothing to do with the weather or NYC. The weather was fine and NYC was fine - well not nearly as good as Denver, but NYC was ok.
The security checkpoints at the stadium were very poorly designed. It took an extremely long time to get through security - no matter where you went - and the lines were not organized well, so it was almost chaos - not quite because almost everyone was well behaved.
That was bad, but leaving the stadium was horrific. Parking was limited as was bus service, and you could not walk to/from the stadium, so most people took the train. I left early, as soon as the score reached 43-8. By the time I got to the area where you queue to board the train, it was already backed up probably over 150 yards (if you had straightened out the winding line; and at times there were 20 or more people abreast. The vast majority of Bronco fans were behind me, let alone other fans, who stayed longer. The overall organization of the train boarding system was the most idiotic system I have ever encountered anywhere. I could spend paragraphs describing the stupidity I witnessed. However I'll save time and show proof by submitting two photos below. By the time I boarded the train at the stadium, there were 10s of thousands of fans already in line behind me. The trains had lots of cars - more than 10 - and each car had two levels, but the boarding system was so asinine that these are all the people in my car - one photo shows the upper level of the car, the other photo shows the lower level.
As you can see (I hope - not used to posting photos), there were maybe 20-25 total people in my car, which had around 120-150 seats, plus standing room. It was not because people were slow boarding, but because of the totally idiotic system that did not let people through. Note - they never checked for tickets or security when leaving - it was entirely the fault of the system. It was not just my car - many (most?) cars was were far from full - while there were tens of thousands of fans in line behind being forced to just stand and wait. Who knows how long it took them to get on a train??
Bottom line - the people who run the Super Bowl are totally incompetent regarding mass transit - and very inefficient at organizing entry security, since it was not due to a shortage of security people. The number of security people standing around doing nothing was incredible, both before and afterwards. Actually, after the game it would have been better if every security person stood aside and did nothing, because the employees associated with boarding the trains were hindering the process! There should never be another Super Bowl in a location where fans can not walk to the stadium.
At least the insanity, of leaving on a train car filled to about 15 percent capacity, with tens of thousands of fans behind in line, gave those of us (very sad Broncos fans) who were on the car, great laughs as we made jokes about the lunacy.