On the other hand, you’re implying that they should maintain patches for every single version of iOS released? Because every minor includes new features. That’s asinine.
LineageOS, a free, volunteer-run open source mobile OS, maintains and backports security patches for n-2, n-1, and n Android versions for phones.
Red Hat, the maker of RHEL, a paid, open-source OS — and its free, open-source duplicate CentOS — maintains and backports security patches for 10 years.
Microsoft Windows 10, a paid, closed-source OS pushed aggressively by Microsoft to the point of being sued, bundles feature and security updates on users like every real-world installation is for beta-testing. The LTSB branch is not available/accessible to individual users, and it looks like that will also start bundling feature updates with security updates.
Apple's iOS, a paid, closed-source, locked-to-hardware OS that supports devices sold in the past three years bundles feature and security updates and aggressively pushes updates on people's devices. There is no LTS branch of iOS.
It's not like the kernel and drivers are spread across disparate layers of the iOS stack. It's not like iOS doesn't have libraries and system services and thus has to duplicate code across disparate layers of the iOS stack. It's not like Apple can't or doesn't have special code accessible only to Apple's apps and iOS internals.
As of right now, there are only a handful of hardware configurations iOS has to support, and a single software configuration. Compared to the tens of different hardware and software configurations LineageOS has to support, or the hundreds of different hardware and software configurations Ubuntu and Red Hat have to support, or the thousands of different configurations Microsoft has to support, Apple's job here is a lot easier.
The gnu/linux stack is richer and more complex.
Compared to other companies Apple does an amazing job of supporting older hardware.
I feel like it’s a double edged sword, if Apple devices didn’t get updates people would complain, Apple updates older devices and people complain.
I think the route they have chosen is the best for most normal none techie consumers.
That is totally sustainable. It's effortful — and they can get away without doing it — "when they can just tell everyone to upgrade to the latest build". Just because they can do something doesn't mean its alternative is not "sustainable".
> Less required QA, less wasted engineering time.
For the vendor yes. More headaches for the user when features they liked are removed or features they didn't like or want are pushed on them. But that was already accepted as inevitable when buying into the Apple ecosystem, which brings me back to my original point: non-user-hostile software.
In any case, I'm not sure why anyone should care about saving money for Apple. As a consumer I should look for the best deal for me, not ways to funnel more money into their pockets. They are very capable of taking care of that themselves.