Huh? Steam is a platform for Windows games and was built because MS didn't offer such a thing. Their handheld devices run Linux and a Windows emulator.
I don't think they ever cared about Macs. The Mac gaming market is vanishingly small. Windows gaming is bigger than all other platforms (including consoles) put together.
Valve focused on Linux because their SteamOS is based on Linux, and macOS competes with it. Mac Steam is Intel-based, not Apple Silicon, yet.
Huh? Steam is a platform for Windows games and was built because MS didn't offer such a thing. Their handheld devices run Linux and a Windows emulator.
I don't think they ever cared about Macs. The Mac gaming market is vanishingly small. Windows gaming is bigger than all other platforms (including consoles) put together.