I don't mind re-using old systems or piecing together an old office system into a gaming PC, but that's missing the point entirely. Sure it would technically be capable of playing games, so would any old PC running an emulator.
However I think the PC gaming market is in a very sad state when settling for a system with an 11 year old CPU that isn't supported in Windows 11, and a 10 year old graphics card that no longer receives driver updates would be over $300 with RAM and an OS installed.
A majority of people aren't going to mess around with an old PC and go through the effort of workarounds to get W11 installed, and an emulator with games installed.
The purpose of the Steam Machine is a system that can already run Steam games you own, sure it doesn't have a 9800X3D and an RTX 5090, but according to the Steam Hardware Survey, the hardware it has is as good or better than what most users have. Sadly the RAMpocalypse has ruined any chance of a first party Valve SteamOS powered desktop PC getting any traction in the market vs. Windows PC's.