I don’t think the point was ever to have to buy the hardware from valve, or that’s not how I saw it anyway. They wanted other manufacturers in on the steam machines, I think there were even units produced. The idea (aside from more steam sales) was to standardise PCs around specific performance levels so developers could target them without the faff of having to know how a 12900K stacks up against a Ryzen 7 7800X3D or a 13700 with a 3080, 4070Ti or a 7800XTXxXTTX.

This game is certified steam medium tier, I have a steam high tier machine, I will get xyz performance.