Hi, I get asked this all the time.
First off, you don't need to learn anything that doesn't benefit you directly.
But learning music theory will not only help you with your own tracks, it'll also allow you to communicate your ideas with the rest of the music industry.
So if you care about building a fanbase and selling merch, you need to learn music theory.
That's a whole lot more accurate than saying all self-taught musicians need to learn music theory. In my humble opinion. 🙂