We have free market for labor. If $20 doesn't get anyone then try $21. There is no set correct amount a job should pay. The job pays whatever the market rate for labor is at the time.
This comes as shock to a lot of Freepers that are old school and think a job pays x then find someone who will take x. That is old school 20th century baby boom thinking. The labor vs jobs available are now even or slightly in favor of the worker so management is freaking out instead of acting like rational humans and adapting. Management has been in the driver seat so long they can't comprehend the change.
As an economic libertarian I agree. That’s not really my question. The market is the net result of innumerable factors and, as I’m sure you know, the genius of the market is its ability to boil them all down to price. I just puzzle over what some of the most salient factors are that drove such a sudden change in the price of labor.