I had recently read a book about the 1918 flu, and it had made the point that these urban cities, at the time, required a constant influx of workers, just to replace those deceased.
So, to actually increase the labor pool, required a tremendous amount of human life.
I suspect the higher disease loads and lower fertility rate had a lot to do with that. But maybe not that things were better in rural villages either. Considering all of history rural areas had higher but the population wasn't increasing very fast. That is until you had mechanized farming.
So, to actually increase the labor pool, required a tremendous amount of human life.