If I recall, the Steam Machine was attempted over a decade ago, 2014? Though, it failed. Anybody have any insight into why it never really picked up? I guess Valve's offering couldn't really compete with the rival consoles at the time.
I know someone has already answered, but in the main it's because Linux at the time had very little software support, particularly gaming. The original concept was based on developers writing Linux versions of their games which didn't happen. They were based on Steam OS 1/2, (still out there for download from Valve), build by hardware Partners NOT Valve (Dell, Levovo etc.), were quite expensive for the time, not a fixed specification so the experience varied per machine and then peripheral support was bad. The original 2015 Steam controller, which was born of this initiative was a 'marmite' device. Most people did not like it (I have mine somewhere still).
What has changed is that Linux Desktop is much better now, even those that have had the Steam Deck since launch will tell you the experience on Steam OS has improved massively. The new machine is build by Valve, with learning from their other hardware they manufactured over the years. But mainly because of this software layer called 'Proton' which allows Windows versions of games to run on Linux with minimal latency. That and Steam has grown massively meaning Valve are well placed to leverage those customers with their massive software libraries.
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