Constand readers of these pages know of my own aversion to sequels and continuation for its own sake. Shea Hennum has a great post about the psychology of such things, in re Firefly:
[D]emanding that something you love continue on for as long as you want because you love the IP so much is such a selfish thing to do. Things like that very quickly reach a point where the material isn’t even good, and the only reason for it to stick around isn’t because there’s something it wants or has to say but because you want it to and your fear of endings is ruining the Mass Media landscape for the rest of us. ... You don’t want the work to stick around because it’s so good and it has much left to say, no, you want the work to stay around for you. You want whatever to haunt the world like a spectre because you can’t enjoy what you’ve been given and resist the urge to wear an idea down to gross nubs.
But this is, I confess, an angle I had never thought about before. Or rather, if I had thought about it that way, it had only come to me from the creator's side. If a creator gets some great idea for a story and then just wrings it dry for decades on end, that to me is selfish behavior; it implies that he cannot leave well enough alone.
One of the uglier sides of this sort of thing surfaced when I read about how Edgar Winter, shortly after a bout in the hospital for a liver ailment, said something to the effect that being in the hospital was one of the few times in his life he wasn't treated like an [expletive deleted] jukebox. That made me think of all the voice actors who have to endure fans begging them to say that line in that voice ... or authors who get pestered with questions about when the next book in the x series is going to come out.
Fans too often unthinkingly dehumanize the very people who bring them such great things. They focus, if not always intentionally, on the artifact rather than the person or even the process. Nobody here is being evil, just thoughtless, but a little thoughtlessness goes a long way, especially when multiplied across thousands of fans.
But I also think this emphasis on sequels implies that the creator has a certain lack of confidence in his own creative power. If someone is being paid good money to produce sixteen books in a series, I'm not going to say they don't have a good deal going, but I am going to feel dismayed at how they've traded up the chance to produce fifteen other things, too — any one of which might be at least as good, if not better. Another of the reasons I'm skittish of turning this into my day job: the less I have to make my livelihood depend on something that could well be unmarketable anyway, the better.
One of the reasons I impel myself to do something new every single time is because of the promise of new and completely fresh territory. I'll have no choice but to produce something different — and what's more, to learn something different.