I'm not sure how to put this nicely, but you can't expect people to continue to support software on an OS version that is essentially End of Life from a vendor standpoint. It'd require that they have an older Mac OS system to test on. It's much easier right now to test on Windows and Linux thanks to the Windows backwards compatibility and the Linux Steam Runtime which make older libs available on newer systems.
Apple's decision to do things "their way" just makes things harder.