Yea, this is the bigger problem: 3rd party software developers drop support for "too old" operating systems WAY too early. Especially on mobile. Some developers only support one major previous version, which is insane.
So, Apple leaves old hardware high and dry by not supporting them with operating systems, and 3P software leaves users high and dry by dropping support for operating systems. It's like they are working together to create e-waste.
I'd argue it's a bit of both. In my case, I have an iPad 3, which runs iOS 9 compatible apps, but iOS itself doesn't backup the app files, so when various developers pulled their files off the app store for those old iOS versions, I lost access to the old software that did work, which really doesn't make want to buy another iOS device. Less of a problem on mac though.
If they're working perfectly, why does it matter if they have current operating support? It doesn't seem like you're dependent on Apple.