Some years ago, I was hearing about people switching from PCs to Macs all the time. Later, not so much, but macOS was still getting praise. Maybe Apple looked at the conversion numbers at that time and decided that the cost of keeping up the quality of macOS wasn’t worth the few PC converts they were still getting, and they figured that not enough people would switch back to PCs since the iOS system lock-in effects, etc. would present enough of a barrier.

So it’s not that there aren’t still people who could conceivably switch to Macs, it’s that Apple decided they didn’t need more converts quite as badly anymore.

Still, only my theory of course.