You could imagine jobs that teach you nothing. We can call that toil. Payment for toil makes folks resist automation. Those jobs require automation, not human toil.
The labor union might resist, but why would the toilers resist getting a better tool?
Those tools tend to make fewer people more productive with less toil, often followed by increased payment in competitive markets.
Payment for toil is a signal to the market regarding which jobs require automation. It is both an easier to measure and more accurate signal, than whether the worker is learning something, to determine automation priorities.
Why progress in the dark?
Theyre sure to resist the machine entirely replacing them. Determination of what toil is can't be made based on pay, it has to be identified by toilers and communicated to automators, a process pay interferes with.