I guess while it's frustrating in some ways for us as fans, I can understand it.
I have some friends who are still patiently waiting for me to finish off writing the novel I started back in my college days (and that's over 15 years ago now!
) Meanwhile, I'll occasionally do a little work on it, get distracted by one of my other projects, go back to it, find that inspiration's lacking at that particular time, or that my characters have taken an unscheduled vacation from my head without telling me first, and go off and work on something else. If the inspiration's not there, sometimes there's nothing you can do about it except go with the flow and get back to it straight away the next time inspiration strikes.
Our boys are always worth waiting for.