Sure. Consumers like this and Steam likes this, because they get a cut of everything on their platform. But game makers are maybe not so interested in having their industry collapse into a monpsony situation, where their choices are 1) give Valve whatever Valve wants and accept whatever Valve gives them in return, or 2) don't make games.

Free markets don't promise perfect efficiency in each case. They promise to be reasonably efficient on average. They also don't promise perfect happiness for just one side of the market; they're a means of reaching a compromise between all participants.