The certification is essentially a teaching degree. This is not a small task and with the price of college, not a minor expense.
Right you are. But it need not be that way. To get a good grasp of, say, chemistry, you really do need four years of study.
But to get a good grasp on how to teach, one semester should do it. That's it. During my first year of teaching I relied on a little 20-page booklet called "Teaching Effectively". No jargon there, no fads. Just tips on how to manage student behavior, how to make each lesson interesting, and how to question effectively. It was really all I needed.