> people are literally paid to spend time on the product

Well, that's just a job. It's the people spending their time voluntarily on a project who are the few that really care.

Also often a project team develop blind spots; I'm on an internal initiative at work helping out another team with some long-standing performance problems, and it's remarkable how much a fresh pair of eyes helps. It challenges assumptions and asks basic questions like "how does this work exactly" and "why are you doing that".