That's probably because outlining, when it is taught at all, is taught in a very specific and didactic way. There is little room for personality when you're following the teacher's rules for outlines. Like little Stepford Students, we learned that a passing grade came when we described the prescribed Intro, Three points (with at least three supporting points each!), and Conclusion. Yippee.
So, I'm guessing the minute you didn't HAVE to outline, you didn't.
But now, three years or three decades after you suffered through your last outline in English class you may wonder if there is something missing. Something in your approach to writing that's a bit willy-nilly. You might even sketch out an outline from time to time, but I'm guessing it doesn't get you where you want to go. An intro, three points, and a conclusion might get a B+ in high school, but it probably won't lead to a compelling sales piece or presentation.
So is there another answer? Something between the chaos (and occasional genius) of unplanned seat-of-the-pants writing and the rigid barriers of the perfect outline? Yup. Storyboarding.
You might wonder, isn't a storyboard an awful lot like an outline? Sure; the storyboard is the unruly cousin of an outline.
Where an outline tends to be very linear, a storyboard is organic. An outline has a standard path (Well, if you're feeling frisky you can reorient your outline so that the AAABBBCCC structure becomes ABC ABC ABC, ooh, fancy). A storyboard has no required flow. An outline, in its perfect form, is extremely uniform and parallel. If you have four supporting points for one idea, it looks naked to have only one sub-point on the next.
A storyboard is tactic, a process. You a play with your ideas, move them around, and see what works. Go digital and create the big blocks of your message in traditional tools like PowerPoint or newer apps such Trello, Scrivener, or Paper. Go low-tech by jotting your ideas on sticky-notes, and then use a whiteboard or empty table to see everything at once. Combine text, graphics, photos and your best caveman drawings to express your ideas. Invite others to contribute and play. Whatever your preferred method, as you group, sequence, and re-group, you find the heart of the story you need to tell. You become aware of the flow of the story, not just the logic-tree of individual topics of an outline.
An outline tends to suck the creativity out of the process of creation; a storyboard lets you bring fresh eyes and a fresh spirit to your business writing. A storyboard focuses on the story, not the structure. Where the outline invites convention, the storyboard invites invention.