An author’s career needs consistency. If you thought you could write a fun mystery and then a Young Adult romcom and then a literary novel about Henry VIII, and then a nonfiction book about the inner workings of a snail, you are jumping around too much for a publisher to know what to do with you. Pick one thing and stick with it. They want to build you. They don’t want to have to start over each time. Your next book should be a suitable followup to your last book.
Authors may protest that they have more range and want the freedom to do other things. You can do that, but consider that you will lose readers, and you won’t be known for any one thing. That matters simply because that’s how the publishing business works. If Taylor Swift suddenly decided to start singing opera, she would lose fans. She might gain new ones, but not enough. And your audience wants to know they can rely on you. If everyone is looking forward to Taylor’s new album, they don’t want to find out that she went off and did something weird. They want more of the same. Of course you can expand on what you’re doing. Just keep it in the same wheelhouse. Sgt. Pepper was a far cry from the early Beatles. They grew and changed. A lot. But they still sounded like the same band. They stayed true to themselves. And it’s part of the reason they are still around.