Chrome OS is reported separately, but it's still a Linux-based desktop operating system (built on Gentoo, as I understand it). Reporting these results as only 4% minimizes the success of operating systems using the Linux kernel.
I dunno, I prefer it this way. ChromeOS is like Android, it's there because the manufacturer put it there. Proper desktop Linux is usually only there because the user (or their "techie friend) put it theere deliberately. Counting the latter tells us more about how cranky people are about the enshittification of Windows. Cranky enough to put in the effort to install and learn another OS.
Meaningless anecdote: I used Windows since 95. Moved to Linux Mint because one project required it. Dual-booted for a year or two, then realised that the Windows partition was just a waste of space. The handful of times per year that I NEED windows, it's far easier to use it in a VM. I'm using Linux on a range of systems, from Thinkpads to homebuilt desktops to 10+ year old netbooks. It Just Works, and you don't need an internet connection or microsoft account to get it up and running. Boot from USB, hit "install," select a time zone, done.