From my experience, it's very hard to find parents, university students or older teenagers with the confidence + knowledge + competence + time to coach.
Many probably have never done a coaching course, and aren't likely to even when they do end up coaching, which makes it even harder to find 'good' coaches who are teaching the appropriate skills for the level and age group.
Add to that the fact that 90% will only be involved with a team when a family member is in it, which brings in its shitload of politics and pressure to 'toe the club line', and I can understand why it's so hard to find 'good' coaching for juniors at lower levels and younger age groups. It's a bit like teaching - it's a job which is easy to do a poor or average job at, but needs a specialist to do it well.