You are arguing for supply and demand setting salaries. But there is plenty of evidence in the economic literature which finds that is not usually true in real world markets (in fact, it turn out to be really hard to find any market which obeys such a simplistic model. And even when it does, it is usually easy to find scenarios where that same market doesn't follow supply and demand.) So supply and demand is mostly, in practice, just a contributing factor - and should be recognized as such.