I was thinking in term of player base size. But now that I think about it more, player base size makes no difference in the context of this conversation.
Mojave is the last version of OSX to support 32 bit applications ( https://appleinsider.com/articles/18/06/05/mojave-is-apples-... )
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Essentially, all software has a end of life. I'll grant that Apple has done work to maintain their software across major processor and operating system changes, but at some point that support is dropped.
macOS being unix-based doesn't make it less proprietary. z/OS is Unix certified and proprietary as balls.
The bare core of macOS (Darwin) is open source, but pretty much everything people identify with macOS is proprietary code built on top of Darwin. You used to be able to get standalone distributions of Darwin (maybe you still can?) that people built from Apple's source and they were almost completely unrecognizable.