When you force high school kids to work days that are significantly longer than a normal adult to achieve a good GPA and get into a good college, you can expect that they are going to throttle back once they're away from home with way more free time than is normal. From my kid's experience: she was up at 6:30am, in AP classes by 7:30am (three more to go during the day). Classes were done by 3:00, then sports practice…
This is about gunning for the elite/upper echelons of society. Doing that requires working like a dog not just for 2 years of high school and 4 years of college, but for likely several decades after.
It's totally fine if not everyone can do it and that more people try than actually achieve it. It would be surprising if those weren't true, and engineering the system otherwise is just degrading what it means to achieve the result.