I generally like to push back against the idea of "burnout" as a results of a particular training system or prolonged mileage. The reality is that most people stop running after high school because they are not fast enough to run in college and just move on to something else to fill time. This decision has nothing to do with their training or any kind of "burnout" but just the reality that running is going to take up a less important spot in your life as you get older, unless you are part of the increasingly small number of people who are incentivized to continue training.
If you are a runner on a top high school program, I think it can also be a kind of perfect situation for a lot of people to really maximize their running without realizing it. Living at home makes it easier to be more focused on running and school. Also the coach will have his runners for key development periods from ~14-18 so runners can be built up for the training to have big junior and senior years. In college, however, the runners are on their own for meals, laundry, time management, and a host of other real world responsibilities and this can be hard to manage or at least take some focus away from running. Also being thrown into a college program where you may be expected to file into a workout group with more mature runners who are accustomed to the particular program may be a tough adjustment or may simply not work.
I also want to add that an aspect of burnout is also motivation. For a high school runner in a top program, it is likely very worth it to grind out mileage and work very hard because you are on a team with friends you have grown up with and you have a lower threshold to be great. A high school runner running 15 minute 5Ks can be someone who wins races, contributes or leads a competitive team, and just generally feels that whatever investment they make in training is worth it because they are a high level competitor. But in college, you'd have to be a 13 minute 5k runner to have that same level success and the reality is not many runners have that kind of talent. For some, once they stop winning or leave that environment of close friends motivated towards a goal (state champions, NXN, etc) they will not find the training is worth it anymore.
I have probably rambled and rehashed ideas in this long post but I do feel strongly about how often the phrase "burn out" is thrown at high school athletes and used to dissuade training hard. Obviously, a high school athlete shouldn't be replicating the training logs of Jim Ryun or Gerry Lindgren but I don't think it is a bad thing for high school runners to run mileage and even train a little stupid if they find it enjoyable. High school running really is a special environment where you things aren't as serious and you can have some very cool accomplishments with close friends. I just always think of someone who could train at 30 mpw and be a decent runner, 4:30 mile and crack 10 for 3200, but if you throw that guy on a team competing at a state level or trying to make NXN, he steps up and can squeeze down to sub 4:20 and low 9 minutes. Even if the runner never improves after that, either because he's gotten everything out of himself or that the injuries start to rack up, the opportunity to run in college wasn't there without the hard training. And people just find other interests in college anyways, so I am very hesitant to blame coaches.