When I was in college I worked manual labor for 5 bucks an hour. The type of work I did was construction and there was no heat or A/C either. That figure would have to be adjusted for inflation. But I guess that would be $15/hour now. But I am not in need of a manual labor job now. But a lot of people are.
Most Americans are simply not willing to do manual labor jobs for $15 an hour. They can make a lot more on welfare and food stamps and rent subsidies.
This plus the fact that Millenials don't do manual labor. They are all holding out for management positions.