So you "should" pay for example Rob Pike or Ken Thompson equal to what you would pay some junior dev because they invest eight hours of their time each working day?
To illustrate further, as a farmer, I sell grain, not time. The job requires my time to be inputted, yes, but if I put in eight hours of work or two hours of work to produce the same amount of grain, I am getting paid the same either way. Developers can structure themselves similarly, which is to say selling something that is the product of time, not time itself, if they so choose.
The average developer, especially those on the lower end of the pay scale, however, most commonly chooses to sell their time and their time alone. And when you are selling hours just like everyone else, price is going to converge within a relatively narrow range. An hour is an hour is an hour so it is difficult to differentiate if one hour is more valuable than another or how that hour translates into the output, and so it is priced accordingly.
Not relevant to the topic, but this one is not true.
The cost of an item is often linked to how much was invested (because that is linked to how much it took to come to fruition, and therefore, how much it needs to sell at to recoup that investment). It's not only the 8 hours that is invested, it's the previous investment that needs to be recouped. That's one reason behind why different people cost different things, which is ultimately down to quality.
We're back to the initial question but at least we've dispensed with communism in the meantime.