I was pretty close to the situation for a few years and I saw the following. And this is just my opinion. During the first term, he had an open door, worked with a lot of folks very well (except union), and even before Sandy, was doing a very good job. Obviously, his handling of Sandy juiced his numbers and he also made a deal with Norcross/Sweeney/Joe D to only put up token opposition in 2013 (i.e., Buono) in exchange for not going all out to flip the legislature to the Rs (which never would have happened anyway). His sights were set on the WH.
The Bridgegate silliness caught him totally by surprise and he thought it would quickly pass. Let's be honest, it was a glorified prank by a few stupid employees definitely without his knowledge. Absolutely no doubt about this to me. But since he looked like the frontrunner for 2016, this got hyper-politicized and severely damaged him. I believe, when he realized this was not going away and that the public didn't believe him, him essentially said screw you to NJ. His attitude was.....after all the good things I've done, you are going to pin this silly "scandal" on me when I had no part in it? Well, then screw you NJ, I'm just going to look after myself. All of those open doors were shut and he just focused on the WH and then helping Trump.