I understand the idea in principle: there are potential costs for data protection and environmental safety.
But in this particular case:
1. The laptops are being disposed of not because they have physical faults, but because their software is out of date. So there are no toxic materials to be disposed of.
2. These laptops were used by children, for school work. They don't contain state or commercial secrets, so the hard drives don't need to be shredded.
3. Even if there are secrets on the laptops, it's sufficient to do a single-pass erase before install ChromeOS Flex.
I'm really curious: if someone were to give you 1000 4-year-old Chromebooks, of which 200 had physical faults and the remainder had only software issues, how much you would spend (on labor for re-imaging and physical cleaning, and on processing waste materials) vs. how much you'd recover by selling the laptops on ebay.