SteamOS is open source with some closed sources component. But most important think you seems not being able to understand is that Valve provide high support to Open source community, which means it wouldn’t be surprising if they decided to drop a open source phone.
Since when is Arch proprietary?
Steam OS is proprietary.
But Arch contains proprietary firmware, so technically it’s not fully free software either.
SteamOS is open source with some closed sources component. But most important think you seems not being able to understand is that Valve provide high support to Open source community, which means it wouldn’t be surprising if they decided to drop a open source phone.