They are another somewhat closed ecosystem and becoming more closed over time. Better than a TV that runs Linux, (so far still) better than Android, worse than any "real" Linux distribution.
They are mostly on the wrong side in the war on general-purpose computing.
Honestly we could consider Chromebook just as Android. Yes technically they run on Linux kernel but there is so much going wrong. It's far from what everyone think when saying Linux desktop.
ChromOS is Linux in the way that Android is linux. Technically it has a Linux kernel, but that's it. It is not a Linux desktop under your control. It's a strictly proprietary OS you have very little control of. It's not Linux in the way that literally everyone else means the word.
As pointed out downthread this isn't true. It is under your control. All modern chromebooks let you enable developer mode which gives you root access, at which point is is a linux desktop in the way literally everyone means the word.
PS: Someone changed the title of this submission after my comment. It was originally something like "By my count, Linux has over 11% of the desktop market." This statistic is obviously clickbait and false, even if you count ChromeBooks, though ChromeBooks are not what people mean when they say "Linux desktop".
Google has been working on Fuchsia, a new open source OS which in theory can replace Linux as the base of ChromeOS and Android
But it is unclear how committed they still are to this. Some suggest it was just a “keep our options open” project or a “stop smart people from doing it for our competitors” project. They are actually using it in anger on their Nest Hub devices, but we don’t know if they still plan to take it any further than that