The consumer is damned lucky that Apple even bothers to support phones beyond the last two generations.
If they did what they probably should have done, your phone would have reported, "Sorry, this update is not supported by your device," when you tried to install the latest iOS version. Then we'd be treated to even more wailing and gnashing of teeth from people who feel entitled to perpetual updates. Apple literally can't win here.
Edit: I will agree that they could 'win' by the simple expedient of permitting OS downgrades. There's no reason they couldn't let you revert to the last version you were happy with.
The consumer expects "upgrades" to actually upgrade the device, as in "making it better" not worse.
And: Apple prevents us from downgrading once we understand the surprise we got, after pushing for "upgrades" all the time.
Also, the consumer needs updates to keep the devices bugs/security holes patched.