Mr Davidson said the families were shocked by the development.
"The thousands of questions they have about the circumstances and individuals who were involved in what happened at Pike River are never going to come out now.
"They feel immensely thwarted but more fundamentally they were shocked that, where there has been so much fault by people as we now know, that no one carries the can for this at all. They find this incomprehensible."
Mr Davidson said it was "most unusual" for a prosecution of this nature to be abandoned.
"This process is one that's been gone into with enormous thoroughness by the police and the Department of Labour in their combined investigation with staggering amounts of evidence available," he said.
"One would have thought that would have run its course and until two or three days ago that was the case. We now know that the prosecution has been struggling to the point it had real doubts about ... the result and the value of pressing on with public money."
Instead of being prosecuted, Mr Whittall and Pike River Coal offered a voluntary payment on behalf of the directors and officers of the company to the families of the 29 victims and the two survivors.
Anna Osborne, who lost her husband Milton, called this "blood money".
Lawyer Colin Smith, who also acts for some of the families, said the decision not to prosecute meant getting into the mine and recovering the men's bodies now took on a new importance.
It could form the basis for further prosecution as analysis of the bodies could result in manslaughter or other charges being laid.
Mr Smith said that was the last chance the families had for a successful prosecution.