This really doesn't work because there is not enough demand for people to upskill. Even during boom periods like 1999, there were still janitors. Janitors did not suddenly earn more money because white-collar hiring was exploding.
You can look around the world, janitors consistently earn more in countries with a stronger middle class.
What you are calling "boom periods" are not composed of lots of people upskilling and moving into a higher earning partition of the middle class (or leaving poverty). I have no idea why you expected then to behave like something they are not.
