[pilsetnieks]

That's just an unfounded blanket statement. There have been wild jumps in quality as well as incremental improvements and incremental deterioration in places.

Take, for example, iOS 7 which came out 7 years ago. On the one hand it brought some sorely needed modernity, on the other, it replaced a well-polished, albeit dated, style. However, on its own UI-wise it was really bad. Subsequent releases have had tremendous improvements to its many faults while introducing others, and I can't see how that could be called "a steady decline."

[stock_toaster]

In addition, I hypothesize that as existing users tend to age[1], that they typically desire less change. However, newer and/or younger users entering an ecosystem may desire other things, such as the appearance of modernity or newer stylings (eg. "Not your parent's OS"). MacOS 10.x has been around for 20 years now. iOS for 13 years. Even if you were to assume that the "core segment" was 20 to 40 year old working professionals (just an example), a huge cohort has moved into, and another out of, that segment over the past 10+ years!

This is seen in many areas outside software, so I would imagine it exists here as well.

[1]: Both age as in their physical age, as well as age as in a "have been users in this ecosystem longer" sense.

[Nition]

This doesn't affect your point but just a note; they're officially on MacOS 11 now.