the issue with chromebooks is most of them are given by schools or are bought because they're cheap, and running a server on them, while it may be possible with command line, wouldn't be the best idea because of the cheaper hardware. An AMD A6 or Celeron will only go so far.
Your argument about security isn't necessarily true either. It doesn't matter the OS, if someone wants to exploit it, it can be exploited if tried hard enough. The only reason why windows seems less secure is because the amount of market share it has and the vas amount of dumb people that download stupid things and run it. ChromeOS seems more "secure" because they make it harder to run any software you want, like hosting a CC server.
Trust me, if linux was more mainstream on desktop market share you'd probably be seeing people deleting their entire hard drive by clicking on that one ad on youtube because tits.