I think the issue here is that the game developers may not have any contract with PRS. Historically they wouldn’t have had to - they’d license the music from the big music labels, stamp their game onto a CD and sell a product. Now they’re not just selling a product - they’re licensing access to a “performance” of it. Valve is the playing an active part in this by “performing” the works on demand. It seems stupid to me, but that’s the world of content licensing.

But with Steam you haven’t purchased a copy. First sale doctrine isn’t likely to apply. You’ve purchased a license for access.