In this case Swift is being used on the server, so that could be an officially supported platform[0] which if I recall correctly is macOS, Ubuntu, CentOS, Amazon Linux 2, and Windows as of Swift 5.3.
I get that, but it still doesn't explain why the above poster used the MacOS market share as a detractor in this case. If you value languages that don't dictate hardware/software for you, then Apple was probably never a serious contender for you.