Conventional wisdom ... conventional commercial wisdom ... is that in the business of writing, when you have a good thing, stick to it.
It is enormously difficult to break big in the business of book selling. As an author, if you have a character or world that sells ... you stick to them like glue (I save my good similes for the books).
This is in no small part why we often have fantasy series spanning 10 or 20 ... sometimes 50 novels.
It's not a bad thing. I've read as many as 7 books focused on the same character and enjoyed them.
However, when it comes to writing I like variety. In the Broken Empire trilogy I wrote about Jorg, a dark, intense, fearless and violent young man. In the Red Queen's war the main character, Jalan, is a coward with a short attention span and little ambition. Those books allowed for a lot more humour than the previous trilogy.
Even with the following wind of a successful first series it's no small thing to carry your readership with you to follow an entirely new character. The Red Queen's War is higher rated on Goodreads than The Broken Empire, but many of the readers who came to it open their reviews with the complaint that "he's not Jorg!". I understand the psychology behind that reaction, but at the same time I have to point out that those same readers don't open any other author's books with the complaint "he's not Jorg!" We are, to some degree, programmed by publishing to expect the same thing from any given author. This is partly because that's what publishing generally wants and gets. Publishing is increasingly a numbers game where the goal is to minimize risk. Risk is minimized by repetition. More of the same is very appealing when that 'same' includes profit.
So I count myself lucky to have publishers who have been willing to let me jump the rails.
And now The Red Queen's War is concluded, what next? Many readers will hope for more from the surviving characters, or more of the Broken Empire's world, or both.
I'm certainly not saying that I won't ever return to those shores or follow the adventures of a favorite character from the previous stories (major or minor). But, just as I didn't want to be bound to Jorg Ancrath for the whole of my writing life (I could be finishing of book 9 of Jorg's saga right now and I'd likely have a healthier bank balance because of it), I also didn't want to be bound exclusively to the world and magics of the Broken Empire.
So, I was very glad when both Ace and Voyager wanted to publish Red Sister and the rest of the trilogy I had started on, (series title: Book of the Ancestor).
We have a new world, a new protagonist, and once again I face the challenge of bringing my readers with me while attracting new ones. And yes, there is no Jorg, there's no Jalan, there's no familiar world. But all these things are also true of every other book not written by Mark Lawrence (of which there are quite a few). And in the plus column, you know you like my writing, and you know I won't keep you waiting. I'm half way through the final book of the trilogy and fully expect to be finished several months before the first book hits the shelves.
After that? I really don't know. I will stare at a wall and see what pops into my head. Everything is on the table.
To conclude: Yes, I would probably sell more books by continuing to turn the handle on the first thing I wrote. No, I'm not doing that. This way lies more fun, more variety, more possibility.