For companies it's not a big deal because their users know what responsibility is. And you can fire them otherwise. Schools don't have that privilege.
Remember, most people at work are not responsible for their computer working. In IT we are because we're doing more advanced things and we're technically able to keep it working and to fix it. However, the HR person, the sales person, etc they are not. And most countries have laws where the employer has to provide working tools, the employer is responsible for providing you with a working laptop and if it breaks it is their responsibility to fix it.
Add to that that without chromeOS you've essentially got one choice: windows. So you'll be finding out all about spyware that rootkits the OS, and constant amazement at just how many different rootkits kids can get installed on a single machine. Hell, when I was in school, I wrote a custom rootkit (bo2k like) and installed it on machines. That was fun and instructive.
(I know technically you can make it work over the internet but it takes very capable admins to make that work)
And yes, I hacked the school, but that was through unsecured shared folders and seeing a teacher enter people's grades in excel, not through the rootkit. That I was caught doing (because I decided to "expose" the school by giving a friend's sister her grades 2 weeks in advance, and their parents went to management. I was in detention "for the rest of the year" and I was lucky that 2 teachers demanded I would be allowed to sit my exams because I was the best in their classes)
However, ChromeBooks will also be banned i Danish schools when the new school year starts in August. The Danish Personal Data Authority (Datatilsynet) have just told the schools that they cannot use them after the summer holidays, for more or less the same reasons and their Dutch colleagues.
The problem then becomes: Which laptops can you get in large enough numbers, at a low enough price, within three to four weeks?
Most European countries aren't so lucky, parents are the ones buying the computers, and unless you're into classes related to computing, or at university level, you're not bringing them into class (naturally covid has changed this a bit) only using them at home.
Can they install a Linux distribution on the existing ChromeBooks?