So for political and scientific purposes, the Mexican wolf reintroduction (which is a subspecies of the grey wolf with an "extinct in the wild" assessment, no critically endangered) was considered experimental up to this point. This population was studied to observe the effects of their presence in the area. This change in policy is just the next phase in the recovery plan's project.
Several reintroduction projects have failed in the U.S. because of poor planning, poor science, or just bad luck (Thick-billed parrots, black-footed ferret, whooping crane). Because Mexican wolves became extinct in the wild, there was no urgency to maintain a viable population in the wild. In addition a captive breeding program has been successful in building a large population to support reintroduction projects.