If you have an interest in actively educating yourself:
It doesn’t matter what kind of writing you’re doing—humor, roleplay, fiction, nonfiction, fantasy, sci-fi, mystery, thriller, western... If you write, you will find stuff out.
I just had to look up the history of mayonnaise. Did you know the earliest reference to mayonnaise that actually uses that word was apparently in 1806? Because I didn’t. That may seem like trivial knowledge, but the point is, by writing, you will be forced to learn all kinds of random things you didn’t know. And all of those little things lead to bigger things, and you will learn valuable research skills as well as cohesive concepts, ideas, and history. You will learn to extrapolate. You will learn to question. You will learn to verify. You will learn to criticize. You will learn to follow clues.
So write. To write, you’ll have to read. You’ll go wiki-walking. You will be exposed to notions you hadn’t considered. And you will learn, whether it’s about Urdu honorifics or the origins of the tennis shoe or the history of eyeshadow, you will learn.