Why would you want ChromeOS and not Linux?
b/c you don't have to think about the operating system and updates. I posted about my experience here: https://news.ycombinator.com/item?id=48051902
...basically, I have "nerd cred" and run linux on my desktop, but for my laptop I wanted: disposable (no leaky hard drive), zero maintenance (no kernel modules for sound drivers), battery-portable.
90% of the time I'm wanting `vim` + `git` + `ssh`, and 20% of the time i'm wanting to run some random stuff locally. Chromebook is basically zero friction and 1/10th the price (and 1/10th the capabilities) of a "very nice mac laptop", plus you can pop into a very capable linux VM (w/ passthrough GUI support) without a lot of ceremony.
Windows laptops are out of the question, and pure linux laptops (until only very recently) were of marginal support and low battery capabilities (especially "close it and stuff it in a backpack for 3 days").
ChromeOS is linux. It's a Linux distro that works correctly out of the box, setting it apart quite strongly from all other Linux distros.
With ChromeOS you get both.
I have used Linux for 20 years, but only for development, and I will only develop on Linux.
For everything else (email, files, photos), I want a browser. Used to be Mac/Osx, but got tired of being managed by it.
Just my preference. You can do everything on Linux, just never felt comfortable with it.