You may find other things Apple does user hostile, but they are genuinely pretty good about supporting old devices. I'm pretty sure you can even still sync original iPods on Macs released 20 years later.
The iCloud compatibility page linked above shows that it still supports devices released 13 years ago. The latest iOS is compatible with devices from 2017, and regular security updates are released for devices going back to 2015 -- that's about half the time iPhone has been on the market.
Especially if you believe that they exhibit "declining quality of software", this is a more rational explanation for the error message than a sudden, massive shift in update strategy to require everyone be running the latest software release.
The iCloud compatibility page linked above shows that it still supports devices released 13 years ago. The latest iOS is compatible with devices from 2017, and regular security updates are released for devices going back to 2015 -- that's about half the time iPhone has been on the market.
Especially if you believe that they exhibit "declining quality of software", this is a more rational explanation for the error message than a sudden, massive shift in update strategy to require everyone be running the latest software release.