Microsoft provides 5 years of Mainstream Support and 5 years of Extended Support at no additional cost (cost is built into the initial license fee).
Heck, I would more trust software that says 10 years of garunteed support rather than lifetime support. Too many companies fudge the meaning of "lifetime", and 10 years blows Google's 2 + 1 years of Android support out of the water.
That Apple makes previous versions of my installed software incompatible when I do upgrade should not be my problem.
(That said, I agree there is a problem here, and I think Apple should ultimately be the one who fixes it)
For Windows perhaps, but they sell Office as a yearly subscription.
(Office 2016 works well on Linux with Crossover. Just bought a Crossover lifetime license. Crossover has a decent subscription/license working - subscription is for updates, you can continue using indefinately if you stop paying. Although it is a little expensive.)
That mechanism is not built into the apple app store, which is why they cannot offer it.
There's probably not much platform-specific code in a password manager, but what are the odds it'll work perfectly under their next emulator, or that you can take such an old codebase and just recompile? 10 years ago, the old "pbproj" format was still supported, but the last Xcode that could open them was Xcode 3 (requires OS X 10.5 or 10.6).
Less than 10 years passed between the last Apple IIe sold by Apple and the first PowerMac G5. Or the last Newton to the first iPhone. Or the original Apple I to the Macintosh II. That timescale has big generational changes, and I don't agree that it's realistic for third-party developers to support software that long at no extra cost.
Then it's going to be very expensive.
I made the mistake, years ago, of selling perpetually licensed desktop software with free updates - the economics really don't work, and it's a mistake I haven't made since.