This is a good point. I am a professional social worker. Where I live, it is against the law to use the title "social worker" without holding a degree from an accredited university and registering with a professional college. An undergraduate degree in social work is a 4-year full-time degree, and for one year of that at my school I had to do field placements where not only was I not paid, I had to pay several thousand in tuition (in addition to the tuition for coursework). In that scenario, it's a low-paying field, and my ability to work through school was severely hampered by the requirements of my degree. I also had kids and could not do the work all day at school placement then work at night at the bar that seems to be done sometimes by students without dependents. I did do what I could and for two years worked 20 hours a week on campus, and did other jobs during other years. But this meant cutting back on school a bit, and so it took longer and in the end I'm not sure how much better off I was financially for working while in school. I did it as much for the experience...
I'm currently working on my my Master of Social Work (which is basically the minimum requirement for social workers in health and mental health due to state and federal reimbursement regs.) The full time students in my program take 4-5 classes a quarter AND have practicum 16-24 hours a week. Working is not really possible. In state tuition is just over $18,500 for the (6 quarter) program.
Lots of students make the same mistake I did and enroll part time so that they can only take 1-2 classes while doing the 16-24 hr a week practicum and work part or full time, but in the end it doesn't really save you money since you pay tuition by the credit hour rather than by the quarter. In the end the program will cost me $28,000 over 14 quarters for tuition alone.
And all of that for a job that in this area pays only an average of $32,000 a year : I'd love it if social work paid more, or school cost less but honestly I think it is a bit silly to ignore my desire to be a social worker and the need for young social workers to replace those who are retiring all because I don't have a rich somebody to pay my way through a very demanding and time intensive program. If every one who wanted to be a social worker/teacher (or insert any low paying job that requires a high level of education here) did so we wouldn't have very many people working in those fields at all.