Another angle: in 2019, Apple felt the need to start calling iOS for iPads iPadOS. It's still the same iOS which runs on phones, just with extra iPad-only features that only make sense on tablets. In their minds this extra stuff is worth calling attention to.
This is not the direction you would expect from a company working hard to erase all differentiation between their operating systems.
Absolutely. Now we have macOS, iOS, iPadOS, watchOS, tvOS and audioOS - all decendants of the original Mac OS X. So in fact, Apple diversified instead of merged the OSs.