This is related to the OPT program. I recall it was created by the govt without any act of congress. It is a moneymaker for low end 'tech' schools. Students attend mostly for the chance of staying in the US for 3 years after graduating in 'STEM' fields, which include things like HVAC, and damn near anything.
In detail, I think there was a law that said who could stay in the US and... and... and "others as designated by the Attorney General." They decided there was no limit to this and created the OPT program.