I used to question this, too, but then again, I also sincerely appreciate having a Chromebook that boots in about 5 seconds ... compared to my phone that takes about a minute to go from off to "useful".
I know it doesn't matter for consumers as much, but it's far easier to centrally administer ChromeOS devices than Android devices, too.
The funny thing about that is that my MacBook Pro boots in a few seconds to a full desktop OS, just as my Windows 10 machine does. The cold-boot time of Android is pretty terrible. Admittedly the devices are pretty slow that it boots on, but still.
I know it doesn't matter for consumers as much, but it's far easier to centrally administer ChromeOS devices than Android devices, too.