High school dropout is not necessarily correlated with low IQ.
The problem with retraining people is not their level of formal education, it’s their level of intelligence.
Education can be acquired. Intelligence cannot be. It is quite probably largely fixed at birth, and is certainly fixed by the time one becomes an adult.
Intelligence is also malleable through thinking and learning. I remember reading the story of a black kid who was on trial for murder. His IQ was measured at 64, which was below the 75 required to be eligible for the death penalty.
However, after having spent 6 months with his attorney and having them continually explain legal concepts and his case, his IQ was later measured over 80, which made him eligible for the death penalty.