Valve confirms Steam Machine will be priced ‘like a PC with the same level of performance’
(www.videogameschronicle.com)
Because it's just a linux PC if they did that they would have to stop people buying them to use for general computing.
It's not locked down like a PlayStation or whatever. A lot of the appeal of a steam deck is that it's just a computer with a convenient UI and peripherals, locking it down might have lost them more sales unless they really tried to become full on console providers, but then you're cut off from a lot of the OSS they use and in an arms race with hackers /shrug