There's certainly a mechanism by which an industry can compel its workers not to leave the industry - the cost of retraining. Most countries front-load training for jobs into 2-5 years near the beginning of people's adult lives putting them into debt - but they're often not able to retrain later on, due to debts (remaining loans from the first time, a mortgage, a car, etc) and responsibilities (often having a family). I don't know anyone with a family who could realistically spend a couple of years working part-time so they could free up the time to go to college again.