It's not insane for them to be transparent. When Valve depreciated Steam Play for MacOS, they had engineers very clearly spell out the reason: the MacOS runtime is not stable enough for games. They also called this out when depreciating SteamVR for MacOS, it seems less like a "strategic move" and more like a platform limitation.
There's definitely something for Valve to gain by porting Steam to MacOS, after all they did support MacOS with Proton originally. The work required to fix it for modern MacOS is monumental though, and unless Apple sponsors it I see no reason why it would happen. Once they axed 32-bit execution support on Mac, there was effectively no reason to keep supporting the platform anymore gaming-wise. OpenGL depreciations were the icing on the disappointment cake, very clearly Valve was being told to pound sand by Apple.
There's definitely something for Valve to gain by porting Steam to MacOS, after all they did support MacOS with Proton originally. The work required to fix it for modern MacOS is monumental though, and unless Apple sponsors it I see no reason why it would happen. Once they axed 32-bit execution support on Mac, there was effectively no reason to keep supporting the platform anymore gaming-wise. OpenGL depreciations were the icing on the disappointment cake, very clearly Valve was being told to pound sand by Apple.