Valve is all-in on Linux and their own hardware. They have no reason to invest tons into a platform with an uncooperative vendor who culturally DGAF about gaming. Why run from Windows only to jump into a more hostile ecosystem? You can still run 32-bit x86 games on Windows ARM, you know.
> They have no reason to invest tons into a platform
Maybe not 'tons', but they've got a solid reason to consider some investment: additional sales from millions of Mac users able to access a huge library of games they were previously denied.