Steam is merely a digital delivery system.
The bigger hurdle is porting the games themselves to Linux, and that's going to take a LOT more work.
Since Valve does not own all of the content available on Steam, Valve has no control beyond its own games with regard to that porting.
As others have mentioned, the biggest gaming issue on Linux is that of robust video drivers.
The Linux community , AMD and NVIDIA have a long history with regard to closed source drivers, and both sides have valid points.
I hope this will be the first step in a new direction for that issue, but I'm not holding my breath.
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