A couple things: At Zimmer's introductory press conference and other early interviews the big topic was him being a hard azz, that's all the media wanted to talk about. Zimm shouldn't have changed for Jerry, McCarthy, Micah, or the media, but like Big Mike said when he was hired "I wanted the job". Also, during when Big Tuna came in Zimm successfully adjusted to run a 3-4 when he was a 4-3 guy. Maybe Jerry hired him thinking it would be easy for Zim to mimic DQs defense.
Overall, something isn't right in Dallas if this man wasn't comfortable being himself and doing his thing. Fans will turn on the coaches when they're just doing what they're told sometimes.