Yeah, what I'm meaning is: the first three books were a blast, and were pubished in a short amount of time. You can see clearly the passion of the writer for the work he's doing. In the following books, the passion was constantly diminishing. When you love to do something, when you have ideas, nothing stops you to put them in practice…. yeah, you can be distracted by other things or duties, but you won't postpone them for years. If you do, deep inside you are no more interested in them. And forced thing are forced, there's a limit to the amount of stuff you can be forced to do, especially if you're a rich, old man.