As surely as not all attempts at mediation succeed, there are bound to be governors turned off by a negative experience with a consensus-based process. What exists for certain, though, are governors who simply have not taste-tested this new flavor of public administration. The reasons for that cover the spectrum. One governor is reputedly hostile to his own state's office of mediation, one of whose key figures was a campaign activist for a political adversary. One of the most common is that mediation is the same as arbitration.
Politicians are loathe to engage in a process that can look like buck-passing.
There's a fear that convening a group of stakeholders can look to constituents like ducking responsibility. Politicians don't hang out in back rooms because they like cigar smoke. They want to know answers in advance, so they know how to deal with them. They don't want to commit to a process that requires them to live with the answers regardless of what those answers are. You're talking about a process that is non-traditional.