Why processes and methodologies donot always work?

Processes and methodologies do not always work. I appreciate the importance of the processes but I have seen managers getting so much stuck with the processes that they would ignore the ground realities and would consider you an idiot if you suggest some deviation from the process. There is usually a direct relationship between the usefulness of the processes and the quality of the managers. i.e., the processes are useful only if you have smart managers.