At my high school, at least, they didn't spend any time teaching you how to write essays. They just told you to write one, and graded you on the results.
Odds are, you were taught, just before high school. Most schools teach a very basic style of "tell them what you are going to tell them, make your case in the next 3 to 5 paragraphs, tell them what you told them"
If you went your entire educational career without ever having to provide an outline, or a rough draft, I would be impressed.
I would also suppose that you were never taught addition in high school either. Same reason.