We can't just call them lousy writers?

We can, but only by constructing a very narrow definition of the word “writer”. I’m not just thinking of the folks in the supermarket bestseller rack with their names in big gold capitals here; there are plenty of good writers out there making careers writing more or less the same book, with more or less the same characters, again and again. If it’s a good book, and if they’re interesting characters, this isn’t necessarily a bad thing. Sometimes familiarity is what the readers want.

re: familiarity

And it is often if not always what publishers want.

Still, those writers had to "put on" the characters at some point in order to produce a good (or at least passable) novel, even if they are reproducing the same work in different packaging over and over again.

I'm more distraught by actors cum writers who enter the realm of trash fiction, produce trash novels, and garner six or seven figure advances time and again. Don't get me wrong, I don't dislike them because they are famous; that's a perfectly fine springboard for writing. It's just that they are generally trite or at best sophomoric and yet the public gobbles up their work like five dollar beanie babies on ebay.

-- david j.

Where I work (a nonfiction publisher) there is a distinction between writers and authors. The writer writes the book, sometimes under a work-for-hire arrangement, and may not be listed on the book's cover. The author is definitely listed on the cover, as that author's reputation is supposed to sell the book. The author may have written his book, but not necessarily.

I suspect that happens in fiction publishing as well, particularly when it comes to celebrity authors.

Well of course Michael Caine can't change scripts; he's in EVERY MOVIE!

Who'd have the time?

There is a name for this:
prima donna

Narcisist is another word that may fit as well.

I don’t think it’s that simple. If audiences have a certain expectation when they go to see a Harrison Ford movie, Harrison Ford doesn’t have to be a narcissist or a prima donna to give them what they want, he just has to be in it for the money. And what the hell, you know? Some people will always want to see that sort of movie, and for those of us who don’t (at least not all the time) there are plenty of actors out there who put a higher priority on doing interesting work than they do on milking the franchise. It doesn’t have to be a value judgment.