I guess you also feel: Why is there a need for a football coach - an on the ball football player can handle the job themselves.
Most projects involve many designers, engineers, QA personal, etc - the project manager is key to getting work done. The last thing you need is 10 designers/engineers handling their own job each in their own special way. Unless it is a one man project - the Project Manager in more important than the designers/engineers. The Project Manager herds the cats.
BTW: I am both a designer/engineer and project manager - they are two different disciplines and both are absolutely necessary.
I also work in the same field at a very large company and can tell you that there is a tremendous amount of time wasted by project mangagers sitting in meetings. I'm well aware of how things are supposed to work.