In my experience, most times that happens because management has actually set the parameters in which people are allowed to think and give ideas.
When I work with groups about ideas—and I engage at all levels of the community—I hear endless amounts of ideas that are presented and that people want to follow. They were never given the opportunity. I can tell you right now, I would lay a month's salary on the fact that there are people in Canada Post who would give you countless ideas. They were just never given that chance.