Add the already-developed Mac ports to Steam

The work has already been done to port The Sims 3 and 4 to macOS. These titles are available on the EA app on macOS, but not through Steam on macOS. On Windows, the Steam release of The Sims 4 is more-or-less just an installer for the EA app which you can even use separately from Steam once installed. It would be simple to replicate this behavior on macOS - the macOS port of SimCity 4 proves you can have intermediate launchers between Steam and the game itself on macOS. 

If not, can the team kindly provide the rationale for such a decision?