100k a week for a 17-18 year old athlete who focuses on the longer events is that much volume. I was doing about that much my senior year of HS (I was a little young for my grade, too, so I graduated at only 17) and never thought I was training at a particularly high level. I did what coach suggested (and they were always suggestions, never commands) and the numbers fell where they fell.
But I mean, a pretty typical quality day of 3mi warmup, 5mi worth of interval work like k or mile repeats, and a 3mi cooldown is already 11 miles (more than 17k for our metric friends). Assuming the athlete just jogs 45min the next day to recover, that's still averaging close to 14-15k a day, or right about 100k a week. From what I can recall from high school, most of my hard days ended up being 10-12mi range (~16-20k) and my easy days were more like 6-8 miles (10-13k) for weeks in the 55-65mi range (~90-100k).
I'm not sure why you think that kind of running is being forced on American HS runners, or that this volume is somehow particularly injurious. To be honest, I'm pretty sure you're a troll mocking the "100 miles a week" crowd by sticking to 100 kilometers a week, but it is what it is.