The element of suspense is another factor. Just like in fiction, nonfiction that reads like it can build suspense. When telling a true historical event, for example, if the writer paces the story well and leaves some questions unanswered until the right moment, it creates excitement and keeps the reader turning the pages, much like a mystery novel.
The main appeal is the narrative style. When nonfiction is written in a way that mimics fiction, it becomes more engaging. For example, using characters and plot - like structures in a true story makes it easier to follow and more interesting. We can relate to the people in the story, just as we do with fictional characters.
It also makes complex ideas more accessible. Take scientific nonfiction. If it's written like fiction, with a story arc and relatable characters exploring the science, it's less intimidating. For instance, a book about a group of scientists on an expedition (real event) but told in a story - like way. It draws the reader in and holds their attention better than a dry, factual account.