Unskilled labor is at a deep disadvantage to skilled labor, why do you think those industries are generally better paid? The more unbalanced the power dynamic the more one side is able to control pricing.

One interesting asymmetry is time - sellers on the labor market typically need to make a deal within weeks or months. Buyers tend to be able to wait months or years. Its hard to say that the market is doing the truest 'price discovery' in that situation.