The issue is that it's impossible for a computer to know what everybody values. When people participate in a market, this allows their values to be expressed: at a particular time, if they spend their money on A over B, then they valued A over B. Talk is cheap (people can say anything they want; it conveys extremely little information if they're not putting their money where their mouth is, so to speak).
On top of this, there is also all the distributed information about the available quantity and quality of goods and services in a particular location. The knowledge that a bunch of good machine parts for a certain piece of equipment are gathering dust in some warehouse can be extremely valuable if that equipment is in shortage, and that kind of data is routinely the source of profit to enterprising people in the real economy. It’s impossible to gather and process all that data and to make it available to everyone. It requires a distributed effort of people and firms acting in their own interests.
No, market participation just requires constraining one’s values to the options afforded by the market system. E.g., lots of people would be willing to take a pay cut for an extra day off per week but the job market does not provide that option. Why not?
