Let's look at what makes Chromebooks great: they're dead simple, anyone could use one.
That's good, right? You get your kid a Google Account. They go to school and use Sheets, Docs, and Slides. Do they get an email account with that education account? Obviously. What could possibly be wrong with teaching kids one very locked down tool from their young age? It isn't like kids need to know how to use computers or anything. Let's just teach them how to use the Chrome browser and web apps. Let's get them into a system that is a worse lock in than Microsoft or Apple could ever hope to achieve.
Part of it, like I squeezed in there, is that Chromebooks aren't teaching people. Chromebooks are a browser and web apps. We're raising a generation that will have no clue how to use computers because all they've ever used were browsers and web apps. And schools are definitely supposed to be about teaching.
For the record, though, this isn't really about Google being bad. They aren't I wouldn't want any vendor lock in. At least with a normal PC, you could always get some educational Linux distribution. Maybe it even has a simplified interface for younger students and a more complex one for the older students. That way we can teach children an uncommon skill known as thinking.