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 They run outdated versions of everything until I hear "we need to buy a new mac because we can't use this website for some administrative thing", which is caused by not updating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...