iOS device support has always been a bit of a mystery. In some cases, devices were cut off because of certain hardware aspects (RAM, APU etc), in others it was because the harware had been pushed too far and should arguably been cut off earlier (iPhone 4, iPad 2 anyone?) and finally devices that are cut off for seemingly no reason (iPhone 7).
The current situation is confusing. From iOS 15, anything without an A12 chip missed out on a lot of features that (presumably) leveraged the strong ML cores such as Live Text, Portrait mode in FaceTime and...more detailed Apple Maps?!, but A9, A10 and A11-powered devices still got the update. For someone with an A11 chip, we've now had two updates (iOS15/iOS16) where most of the new features weren't supported. So, why drop A11 devices now when they could just continue to deny them features? Historically, there tended to be some devices that get extra years sipport (generally the S versions of iPhones) - usually because they had some hardware feature that enabled this (faster APU/more RAM in 3GS, More RAM in 6S). Here we have devices that have a decent APU (A11) and additional RAM (3 GB for the iPhone X) compared to the previous generation.
On the iPadOS side, it's clear that the reason customisable lock screens are not supported is that this needs the ML cores (even the weak ones in the A11) and because Apple were recycling the A9/A10 chips in iPads as recently as 2019 they couldn't drop support for them. Thus we get the rediculous situation where an A10/2 GB device (6th gen iPad) looks like it will get OS17 whilst a A11/3 GB devices (iPhone X, iPhone 8 plus) won't.
My take on this is that Apple has been on a downturn for 7-8 years. Less and less devices are being sold year. Apple has been hiding this by no longer reporting unit number sold, bumping up prices and pushing people to buy higher end models. I have no doubt that they have data showing that when a device loses access to the latest OS version a certain percentage buy new devices which may have prompted them to drop more device support. Apple has the money and dmoninance to survive just about anything but when you are pushing prices higher and higher to keep revenue increasing, there will come a tipping point where people can't take any more. In many ways, the monthly pricing helps hide this (remember when iPhone prices jumped from $699 to $999 all the people saying it was only an extra $10 per month), but when increasing prices meets a cost of living crisis something is going to give...
At the end of the day I have to hold my hand up and admit that I am to blame for this: I made the decision last month to get a new battery for my iPhone X rather than get an upgrade to keep me going for another 12-18 months so naturally, Apple act to cut off support within 7 months...