Why are macOS and OS X listed separately? Is it to delineate pre-2016 Macs from post-2016 Macs, when the rename to macOS happened? But in that case, I have a hard time believing that there are way more pre-2016 Macs floating around out there than post-2016 ones, as the chart shows. I have a hard time believing that anyone is running pre-2016 OS X versions at all, outside of a very small group of hobbyists; I thought Apple’s data showed that generally Mac users were pretty aggressive about being on relatively current macOS versions.

Also why separate out OS X and macOS at all when it appears that all Windows versions are lumped together and all Linux versions and distros are lumped together?

All of this seems very suspect.

Anecdata: Every time over the years that my parents (now in their 70s) have purchased a new mac, software updates only ever happen if I run them. I don't visit all the time. They run outdated versions of everything until I hear "we need to buy a new mac because we can't use this website for some administrative thing", which is caused by not updating the os and the browser becoming unsupported over time.

Also account for i.e musicians (I hear there's a few of them in Apple-land) who seem to keep getting bitten by Apple somehow breaking compatibility with a bunch of audio software/equipment even with developer release, time and time again.

Multiply by real world amounts of people.

Would be a good explanation...