At least here I’m pretty sure schools just buy them because they come laughably cheap. Actually, my middle school’s laptops weren’t very durable either but just cheap.
Actually, now that I think of it, Chromebooks can be manufactured by anyone just like Windows laptopa, a Chromebook is just any laptop with ChromeOS pre-installed. There are probably well-built ones (maybe by Lenovo, even?) and there are probably flimsy-made ones, depending on your manufacturer?