Dean Ambrose has as far as I'm concerned anyway outdone himself since the Shield broke up. Here is the only Shield member who didn't have the WWE machine behind him and he's turned out to be the most popular out of the three.
Rollins was hand picked by the Authority to claim the title and quite honestly his title run was a disappointment. He was booked as a chicken shit heel, who need not only Kane but J&J Security to win matches. Reigns, well that's another story. He's had the most pronounced push I've seen in recent years and the guy still isn't over with the majority of fans. Women and kids love the guy, but others, well not so much. Nothing wrong with his look and ring work, there is just no connection.
Ambrose wasn't pushed by upper management, he was jobbed out for the better part of a year or so, and for some reason or other the fans got behind him. Even though he's not won the majority of his feuds, they are still behind him. He's likable, he comes off as being in a strange way, natural. There is nothing forced or fake about him. Basically what you see is what you get. When you see him on other shows he's totally the same guy. And I don't think he cares whether you like him or not, he's is who he is.
Dean Ambrose is also a workhorse, doesn't seem to get injured and as someone else said, he's always there ready to go. I have idea how many nights a year he works, but he doesn't ever seem to complain about it either. It doesn't matter who they pair him up with or pit him against, he always seems to get the loudest pops from the crowd.
Yea he could be better in the ring and he used to be when he was in the indies, he's had to tone it down a lot for the WWE. I think even if he was to turn heel he would get the same reaction from the fans. He also moves a lot of merchandise for the company as well and puts assess in the seats. His B tour was pulling in more fans and money than Reigns did with a better roster.
Ambrose has made the best of a bad situation and the fans like it.