I recently had to add a Mac to my zoo of hardware I'm trying to do productive work on - which prompted me to clean up and document my environment variable importer, which had grown to platform specific functions with lots of code duplication.
On both Windows and MacOS I have properly configured shells with all relevant variables - so it makes sense to query them, instead of duplicating the logic how they create that configuration into Emacs.
On Linux that'd have worked too, but I also have the relevant variables in the systemd user session, and querying that is a tiny bit faster than launching a shell.