Are prolific authors necessarily better or worse? You think JCO is prolific? Try some of the people mentioned in this article, with near 1000 books in a lifetime. What drives them to do it?
Ultimately, we know that all writers do what they can and what they must. Truly extreme productiveness (like its opposite) is beyond the absolute control of the author. For the rest of us, the respectably rather than the manically productive, there are more practical explanations. Partly it’s the freelancer’s conundrum. Anthony Burgess (75 or so books in some 40 years) used to say he never turned down any reasonable offer of work, and very few unreasonable ones. This will be written on many of our graves.
But perhaps the real reason we keep writing is the hope, naïve perhaps, that we’ll make a better job of it next time. Unless you’re a genius or a fool, you realize that everything you write, however “successful,” is always a sort of failure. And so you try again.