Where do they make money on that? The margins on the devices are so slim and go to the OEMs, which Google mostly isn't. I don't think they charge any money for

Where do they make money on that? The margins on the devices are so slim and go to the OEMs, which Google mostly isn't. I don't think they charge any money for OEMs licensing the OS, and if they do it's likely a pittance. The only way Chromebooks make money for Google is as a gateway to Google services, and allowing people to fork ChromeOS like that puts that revenue source in jeopardy.