I disagree.
I spent lot of time and hard work towards my master’s degree in engineering. That is a field where highest percentage of students drop out or flunk out. It is a hard curriculum. Why rack your brains out studying mech engineering when you can make more money by becoming a doctor, lawyer, or even an accountant.
I worked for 23 years for an outfit who designed and manufactured machines which are subjected to the most violent shock loads, more than any other machine in the world. It is called cold extrusion of steel. My team had all foreign born people. American born engineers prefer other routes to success such as management.
A truck driver in America makes a good living. Why suffer the hard work of advanced degrees in engineering.
A small percentage of truck drivers make a good living (unionized UPS-type primarily) - and FReepers have pointed out how even that field is having foreigners trafficked here to take the jobs.
There is no genuine shortage of STEM workers in this country; what we lack is an American workforce that will allow employers to roll back a century of labor reform.