When writers write, it should be filled with their passion. It doesn't matter whether it is nonfiction or fiction, horror or romance, but when a writer writes, they put themselves in the story. It comes from their mind, their imagination, their research, their pen (or keyboard).
Writing is taking a piece of you and putting it on paper. Then, maybe someone else will read it. When they read it, will it show your passion. Will it be a story they feel, they see, they hear, they are a part of, or just a bunch of words put together without any depth or meaning. If you write, you can write what you know, but it's better if you write what you want to know. Do your research on what interests you, then write it. It doesn't have to be a major part of the story or even a genre. Case in point, I am a big fan of Star Trek (most of the franchises, with TNG and Voyager being my favorites), however, I don't write Sci-fi (but maybe one day I will try it).
I write about what I like to write about and if something comes up that I don't know about, I learn about that. In my M.O.D series, there are a lot of law enforcement officers, doctors, lawyers, social workers, chefs, and I've never been any one of those, so I learn about those occupations. I do my research. I don't have to do each of those jobs to write about it. I also like SuperHeros, doesn't matter if it's DC or Marvel, I love Superman, and The Flash, The Hulk, and yes, even Wonder Woman. Some of my characters like them, such as Terry Markum is a big Superman fan, and his wife even made him a cape (for their own personal use). I like the show Supernatural but also cop shows and action packed movies, like Lethal Weapon, Law and Order, Criminal Minds. I also love the old shows Hogan's Heroes and M*A*S*H. What I like inspires me. What inspires me can become a story. I don't write fan fiction, but there's nothing wrong with those that do, unless they break the rules about that. I did once, however, use the names David Banner and Jack McGee (character names from the show The Incredible Hulk) in my story and their names had a purpose and so did their characters.
Names, character depth, backstories, forefront stories and stories to come, they all come from the mind of a writer that has passion about his or her work. I don't have to be a private detective to write about one. I don't even have to be a Hippie (Savvy) or a Police Detective (Carly Edwards, Rayna Larson) or even an accountant turned profiler (Andrea Wallace). I am a writer, just like Link McLaren, but I don't write without wearing clothes.
Write with passion or the writing has no depth.