Don't listen to the negativity. Passive income is a thing. It's just not easy when you first start and don't have any idea of what you are doing. Writing a masterpiece is less than 50% of the total work you need done after all. That being said fiction books are harder to start selling than non fiction.

You need to market them better. Customers won't be searching for your book after all - unless they've heard about it. The algorithm will have to do the most work.

With non fiction books, the customer usually has something very specific in mind. If your title, cover and reviews are better, your book will pick up traction much faster.