I truly appreciate the mail that I get asking for further adventures for many of my characters. I'm honored that you like them well enough that you want to spend more time with them.
As much as I enjoy all (well, most of) my characters, once I finish a story, I want to move on to other people in other situations. Once a book has been published and out for a while, with readers deciding for themselves what happens after the end of the story, it hardly seems fair for the author to come back and say, Nope, you're all wrong--THIS is what happened next.
Besides that, one of the reasons I became a writer was because I enjoyed mentally writing sequels to books I didn't want to end. (Or I made up new endings for stories I felt ended the wrong way.)
It's an interesting exercise that you might enjoy.
Meanwhile, I won't say that I'll never write a sequel to any of my stories. But I have no plans to at the moment.
Books that--while not sequels--are linked to each other are