There were two things going on: 1) I had already established in my own mind where I wanted to go with the next series, and having James around as a Grey Eminence would have complicated matters. He had had an amazing life and it was time to bid him good-bye.
I have a huge respect for writers and realise that this is not an area that I find easy. I doubt that I would have the patience in front of a blank sheet of paper to become a writer.