I would point out that the thread is talking about a tiny group of extremely lucrative writers, who are either big names in themselves or are putting out large books in a series for which a keen audience already exists (or both). When you are a small writer, even one with a series, the situation is different. My influence on the literary world is about as small as it could get, but I do get asked when I'm going to write another Smith book.
Last Saturday, I was at an event where this came up several times, and I was just honest with people: 6 books (two trilogies, if you like) is a nice place to have a break, I've got other stories I want to tell, and I'm wary of just doing the same thing too long. I've never met anyone who wasn't reasonable about this, but people are always more obnoxious on the internet, I suppose.
On a sort-of-tangent, years ago I gave a talk at a steampunk event where I described my lead character as "a wally" (ie an idiot). A guy in the audience was genuinely quite hurt that I'd dismiss a character he liked so brusquely, and I had to backtrack somewhat. So, writers are free to do what they like, to my mind - but they should be wary of the consequences, fair or otherwise!
EDIT: Oh, and I should add that you can't truly understand my work unless you have purchased each book at least four times. You can read them as often as you like, but it's the purchasing that brings real understanding.