Older but still otherwise perfectly functioning iPhone models have also stopped working. Let's not get into a platform war here.
However, Android it's not so clear since it's possible to buy a recent cheap chinese phone without the correct carrier profiles that would be falling back to 3G for calls.
If we'd assume that's honest and true, then this isn't an age or practical software compatibility, but arbitrary whitelisting issue.
This is what the original article is mostly furious about.
The way this has been implemented by at least some of the carriers is:
1. Do we sell this device AND we know you can use VoLTE to call emergency services with this: allow 2. computah says no.
So the device being capable of VoLTE and/or emergency calls VoLTE is not enough.
A functionally equivalent iphone might be from an IMEI prefix that was not sold by that operator and denied even tho everything would work.