Subsidization pretty much requires that the hardware be locked down and walled-gardened so the subsidy they put into it eventually pays off. The Steam Machine, currently, lets you install whatever OS you want and use it like a regular PC without locking you into the Steam ecosystem at all.

For this to be true, you'd need to have some data that a significant portion of Steam Deck (to name the hardware that's out for years) users wipe SteamOS and not use it for Steam.