It's not a fraction of what it would cost to actually employ those humans, since there were humans who clearly chose to do that work when presented with the opportunity.

I think this is a very first-world oriented take. It efficiently distributed low-value workloads to people who were willing to do it for the pay provided. The market was efficient, and the wages were clearly on par with those who were doing the work found economical to do, considering they did (and still do) the work for the wages provided.