There's a vast gulf between Android and a Linux desktop environment. Android is a Linux kernel with the Android environment on top and is not just some Linux distro like anyone uses on a PC. ChromeOS is very similar.

Android and ChromeOS are still Linux distros, with a UI dedicated for their exact purpose. There have been other distros in the past trying to explore different ways of building a Linux, Gobolinux for example tried to get rid of the traditional POSIX filesystem hierarchy. Sure Android and ChromeOS probably diverged more but that doesn't make them any less linux distros. For a start, termux couldn't exist if android wasn't a Linux distro as no emulation or vm is involved, these are typical linux userland and processes running on android.

FWIW and for good reasons current Android UI is terrible for a desktop usage and ChromeOS is too limited for some people.