There's a lot of Gentoo hate in this thread. I think that's funny when you consider that the most-used Linux distribution on desktop/laptop computers is based on Gentoo. [1]
Google chose engineers for ChromeOS, and those engineers chose Gentoo. CoreOS also uses portage IIRC. Gentoo isn't for everyone, but I think there's probably a correlation between people who have used Gentoo (or similar) at some point in their life and people who know Linux thoroughly.
ChromeOS originally was built upon Ubuntu, but Gentoo made more sense when starting to build for a rather diverse set of hardware, various flavours of ARM etc.
Google chose engineers for ChromeOS, and those engineers chose Gentoo. CoreOS also uses portage IIRC. Gentoo isn't for everyone, but I think there's probably a correlation between people who have used Gentoo (or similar) at some point in their life and people who know Linux thoroughly.
[1]: https://www.quora.com/Why-is-Chrome-OS-built-upon-Gentoo-and...