I thought the same thing until my son went to Prep last year as a repeat 10th grader. Started on 4th line, practiced everyday with the team, moved up to 2nd line for last 1/3rd of season with PP time. Now has 2 years to contribute valuable time to the team. Sounds like development to me.
Yes, and good for your boy. Unfortunately, it happens less and less.
"Prep" covers a lot of ground. Some schools over-recruit, so that scenario can't happen. The numbers won't allow it. The coach would rather bring in a "hot" 9th grader or a repeat 11th grader than reward an upperclassman for their hard work - on the team and in the classroom.
My boy did fine, as well, but he happened to come in when the team was really short on D, got an opportunity and took advantage of it. The next year they brought in some really good players that haven't seen ice time, because they were recruiting players each year that slotted ahead. I honestly don't understand why the parents kept those kids there. They would have developed way more playing full season. Now, they're done in the sport come June.
Staying because they are happy with the academics maybe? Matriculation rate to top colleges? friends ?