Why do student teachers receive payments of either 1) pennies or 2) nothing at all?
Having been a teacher myself, I have had student instructors in my classroom. It takes a lot more labor to have a student teacher than not to have one. They don’t contribute much to the classroom and require a great deal of help and direction. It isn’t the same as having a teaching assistant or second instructor present in the classroom. (In other words, they make photocopies, are pleasant to be around, and are safe, kind adults to their pupils, but generally they aren’t performing important job.) They are essentially receiving job training through an internship. Although teaching doesn’t need much science, it does require a great deal of practice because many distinct parts must be learned at once. You cannot learn it from a book.
Not because I’m getting important free labor, but rather because I know that my community needs fresh teachers to graduate every year, is why I take on student teachers.