It is the activity itself and sharing one's results with students and colleagues that faculty members find rewarding. Being a faculty member is not a job, it's a life. In response to those isolated cases in which faculty members do lose their commitment to learning and research, the best action is not to dismantle the tenure system, but rather to take the necessary steps to deal with individual cases. That is why many progressive universities are considering the issue of post-tenure review. Post-tenure reviews of different types have been adopted by dozens of universities nationwide, including state universities in Texas, Florida, Wisconsin, Georgia and Arizona.
Some universities make such reviews mandatory for all faculty after a given period of time.
I believe that is a mistake. Rather, post-tenure reviews should be undertaken only when evidence exists to warrant them. The primary goal of the review should be professional renewal. In cases where a faculty member's commitment to learning cannot be regained, termination may be appropriate. However, that process is distinct from post-tenure review, and must follow all the legal and moral strictures of due process.