Why are some stakeholder roles not represented in some organizations that practice the Six Sigma Methodology?

I noticed, that after practicing Six Sigma in more than one company, that all companies value all the roles to a project and others seemingly don't. Again, operating word is 'seemingly'. And, I believe this is so. Some roles are merged in some environments not because they belong together or logically merge, but for logistical reasons.



I still think that when learning the basics of practicing Six Sigma, one understands the role of each one of the stakeholders to a project. In fact, it is important to declare responsibilities of the roles in order to ascertain that this role's view is properly represented in the project.