The only reason I even have to "upgrade" to a higher version number is how quickly app developers (including Apple themselves) drop support for older OS's. My iPhone which is stuck on iOS 15 runs just as well as the day I bought it, but every other app I download tells me (in essence) "LOL your phone is too old and our developers are too lazy to keep our software running on it. Upgrade your OS or get lost loser".
That's literally the only thing motivating me to upgrade anymore: The treadmill of software compatibility. Apple doesn't have to innovate--they just need to make sure the ecosystem is broken after ~5-10 years or so.