This is a topic I've considered a lot. A lot of people with knowledge and experience are not approachable. And further, dealing with unhelpful people has set me back a ways in life. It's good you seem approachable. I wonder what your advice is on finding approachable mentors in real life. A lot of this will have to do with personality and worldview too, I find.
I think your right in that personality has a lot to do with it. I also find a lot of academics are quite insular and have difficulty communicating with people outside their field and the general public.
There is also the money aspect, in the fitness industry I know a lot of trainer believe in not giving out too much information in an attempt to build dependence and don't explain the "why" for the training they provide. You see it a lot online with people marketing their training secrets and promising results with their "innovative new training program". A good trainer or coach will explain why they are prescribing the exercises they are giving their clients. I believe knowing why you are doing a particular exercise or training technique builds confidence and exercise compliance rather than just doing it because the trainer said so or it is a current fad.
At the end of the day their are multiple ways to achieve results, none of them are secret or special a healthy beginner can achieve a reasonable level of results with almost any moderate fitness program, it only gets complicated when health issues, injuries, age, or gender related problems come into play or the person is looking to achieve result beyond the normal eg. elite athletes who want all the benefits science can provide where a split second of time can mean the difference between winning and loosing.
I have been an athlete for a long time now, I have made a lot of mistakes as an athlete when I was younger, those mistakes, high training loads and elite competition has had a toll on my body, There is a lot I can no longer do, I no longer look like I was ever an elite athlete, If I can help prevent a younger athlete from making those same mistakes and suffering from the long term effects of those injuries while still performing at a high level I see it as success. At uni the younger students see the injuries and performance issues as theoretical, for me they are a lived experience.