The change from say one version of Windows to the next is tiny, and happens every 5 years or so.

Changing from one OS to another is orders of magnitude more complex. As you point out above jumping between them is painful.

Your job may require you to do that, but you're a tiny sliver of the work-force, never mind everyone else. My book-keeper has never encountered the Windows Registry.

You're thinking of the OS as an actual bit of software you interact with. For 99.99% of users it's invisible. They just want printing to happen when they press the print button.