Simply put, ease of use. They could package more Xbox-related stuff in there, like messaging or whatever. But literally just create it as a downloadable application through Steam itself. I’d assume perhaps the value isn’t really there for MS, but it would give an easier access to their platform.

If they were that serious, they could work on a native Steam/Linux client, even if that was simply for streaming play. Making it easy/simple to get more people on it and into the ecosystem should be an easy win.