Yeah why would valve try to place the steam machine at the gaming pc sector?
This sector is heavily contested by many sellers. And you can’t be cheaper than building your own rig. And on top of that, almost every pc enthusiast has already steam installed, there is no point to build a pc for gaming for valve.
However when you go into the console space things are very different. The steam machine has no problem competing with an Xbox, PlayStation or Nintendo switch.
Now performance isn’t everything, now you have steam on a console like pc. People can play their already owned games and by new ones for playing on the TV.