If some industries are so overcrowded and competitive, why do people keep trying to enter these industries?

Teaching offers a supportive, non-competitive work environment, summers off and a pension at retirement. Those other fields are glamour fields -- people want to be creative and hang out with creative people, actors, politicians, etc. Law generally pays well, although times are tough for young lawyers right now. I have a number of family members working in TV and film and the only one making "meager earnings" is the one just starting out. So it can be done, if you are ambitious, persistent, smart, good at metting people and making contacts and very good at what you do.