Agreed. You should be able to get automated security updates and optional feature updates.
"Should" in an ideal world doesn't equal "should" in a world with deadlines and limited resources. It's enough work to ensure that all the features work with ONE version of an app. If you had to also test every version of the app without this or that feature update installed, you just continually multiply the testing requirements by the number of optional features.
And don't say unit testing solves this problem. The problem is in INTEGRATION testing with the whole app, which 99% of the time can only adequately be done by making the build and having a human use it. Even automated integration tools won't find things like formatting errors and buttons too small for humans to click.
I'd like to continue to maintain ONE app, please, and not `n!` app permutations.
The trouble with today's highly connected world is that it has bred a culture of shipping software that isn't really production quality, on the basis that it can be fixed (or not) later and that's sufficient. This leads to arguments like your final paragraph: you (the developer) would obviously prefer to only maintain the latest and greatest of what you do, but stated without taking into account the consequences of that policy for your users/customers.
While I have a lot of sympathy for your desire, as a developer myself, I think you can only justify that sort of position if your previous releases are sufficiently good that they don't need maintenance. Otherwise, if you have customers paying for one thing, and that thing is defective, and you then want to use those defects as leverage to push your customers to something that is not what they paid for, then I think you're on very shaky ground. There are a lot of ethical, economic and legal issues raised by that sort of business strategy.
I don't like this attitude either, though. Developers have gotten fat and lazy not dealing with any sort of variation in deployment, let alone versions. Everything is all Android or iOS. All Chrome and maybe Firefox. x86 or ... maybe arm. And not be connected to the Internet? That's unpossible!
With hindsight and better tooling we should be able to handle more complexity in how products are used, not less.