Everyone has a comfort zone. Writers in particular have a comfort zone that they tend to stick to over the course of their career. There are valid reasons for writers to continue in their chosen genre. One reason stands out more than others--it's what the readers expect.
How many times have you settled in with comfortable author, confident in what you can expect, only to be disappointed or upset when the story isn't in the genre you expected? I know that has happened to me more than once.
Actually, something very similar happened when my first two books were released. Chrysanthemum was a wild, funny, outrageous book set in an alternate Arthurian universe. Dancer's Delight was not particularly funny. While set in a very unusual universe, the actual story line was more vanilla. Both books were the beginning books for new series. One reader commented that while she really liked Dancer's Delight, it was different. There was a vague hint of disappointment in that reader's tone. In this case, I had moved just a little out of the reader's comfort zone.
Writing out of our comfort zone can energize and refresh us, allowing us to try out new ideas and genres. It doesn't necessarily have to be shocking. If you're an erotica writer, try writing a romance with no sex. Or perhaps you're a paranormal writer, so write a contemporary novel. Moving out of our comfort zone--if we embrace it--can be liberating and freeing.
Sometimes, it can be as simple as answering a challenge. In a discussion with some other writers, we speculated about how far we could carry the concept of were-animals. What would be toooo way out? One person rashly mentioned that I could write about whatever the others came up with... and I did. It was a romance with a were-tick. Actually, it came out pretty good. You just never can tell what you might come up with when you move out of your comfort zone.