One might also consider that many jobs like sheitel-macher, waitress, cleaning lady, and gan morah often do not have job security or benefits. Forget the halachic/ethical issues entailed by many of these jobs which do not exactly go “by the books”, but because of this, employees might never accrue social security credits, or health-care, disability, unemployment, maternity leave, and retirement benefits. Things are great when you’re young and in good health, but what will happen if you get sick? or when you can’t work any longer?
A very yeshivish friend of mine went to law school and has a job at a law firm. When she had a baby, her company continued paying her up to 6 weeks full salary while she stayed at home. She also had an additional four months which she could choose to stay at home without pay, but during which she could choose to go back.
In many of the jobs people here suggested, if anything happens (including having a baby), you are generally not paid, and generally have no benefits to help. What might be useful in the short-term can have dire consequences long-term.