I think one of the issues in doing work with people and their nutrition is that health deterioration due to poor nutrition can be slow. People often seek nutritional advice only after the effects of their dietary choices have reached a place of significant health impairment. Of course, recovery from that point can be much more difficult, and more gradual, than if those individuals had started caring for their nutrition earlier. But I think it can be difficult to convince people who feel pretty good, whose symptoms are present but not severe, that they should take a more active interest in their nutrition before their problems become more serious.
A related issue is that improving health can also be gradual and thus frustrating to people who want quick results. In my experience there are some dietary changes and supplementation protocols that can produce a significant positive change in many people quick quickly. However, overall health is not something that can be improved over night. People that have been eating poorly for a long period of time are simply going to need a similarly long time of eating well to improve much of their health. Nutritious living is a long-term lifestyle, and the earlier one starts, the better.