It's because he doesn't write often. He refuses to finish a series without the publisher giving him a deal, and he's only writing Tiny Tim because he has to pay Niki's mom back. He doesn't do it for fun, or for the love of it; and he likely doesn't have many projects, finished or unfinished, other than what we actually know about. 6 terrible books he's proud enough to put on his website, the two Abyss Walker books, and Tiny Tim.
I had that feeling a lot when I started, ironically inspired by "if Fatrick can do it, anybody can." It goes away once you get a grip on scope and subplots. It's like I said before, most of his books only have 20k words or so of actual content. The rest is padding to fill the space because he's so devoid of actual ideas.