The US Navy was paying $9M to keep Windows XP updated and patched just for them.[0]

I bet if you pay Apple similar amounts of money per year, they'll keep specific APIs available just for you.

And it's not like updating the app to a new iOS version is a massive undertaking, in most cases it's just a matter of opening the project in XCode, adjusting the OS version, compiling and publishing it again.

[0] https://money.cnn.com/2015/06/26/technology/microsoft-window...