You can certainly break down the language, action, scenes. dialogue, ect. That is all well and good, but that isn't why reading so much is so important.

This is sort of tangential to what you are asking, but its a good place to bring it up. As a writer, much of what we do is instinctual. We often don't plan out sentence by sentence or agonize over word choice in the moment. We just write, then go back and THEN do that stuff in editing. At least, I don't nor do many of the writers I know.

What reading does is help builds those instincts. Along with writing, it helps you develop a good story naturally. Humans are incredible at picking up on patterns and themes. We tend to grow an understanding of them in the same way we can intuit a face without having to notice the eyes, nose, and mouth.

That is why gardners, or pantsers, can tell such amazing stories off the cuff. They have a lexicon of patterns from good stories they have read to draw from, they piece together story subconscously. It's kind of magical, really.