There is no magical land in the midwest where humans dare not tread that is a bountiful gold mine of productive capacity.
Demand for labor is not a reflection of "there is so much work to be done, if people are willing to do it for no pay" in the same way you cannot claim there is tremendous demand for mansions because most people do not live in them already. Demand comes from financial pressure on suppliers to generate supply. Be it labor, corn, or software. Real demand creates a business opportunity. All the examples you cited are just the exploitation of poor helpless masses for cheap labor to do work that would not be done if people could not be paid so little for it. Its the extra toaster cozy of the labor market, a thing you do not actually particularly want or need enough to create actual substantial demand, but something you will get on the cheap because its there and convenient.
There is no future in that. Economics cannot be powered by the utmost of human desperation and poverty. Well... it actually can, and was for much of the industrial revolution, but with our modern advent of human rights and treating workers like actual people rather than cost centers reverting to the use of the starving as disposable tools would hopefully be a bit repugnant to some.
People move from rural areas to urban ones because there is no demand for them where they came from. The land is utilized, and often constrained by freshwater access than actual square footage, but until crop prices rise enough to justify expensive pumping of freshwater to drier regions nothing will change there. So they have to go where even the slightest potential opportunity is, and that is what has driven people into cities for centuries.