Must have missed his saving throw.

Link

Amazon has a collection of nonfic essays written by SF/F authors, available as downloads for 50 cents each.

For instance, Building Alternative Realities by Robert Silverberg:

During my fifty years as a science-fiction writer I’ve often ventured into the invention of alternative worlds of possibility – history that never happened, but perhaps should have — which I find opens up the sort of infinite ranges of speculative thought that have made s-f so much fun for me. In this piece I explain what the science-fiction genre of “alternative reality” is all about and show, step by step, how I went about creating the alternative world that was the basis of ROMA ETERNA, my most ambitious work in that form.

There’s also a blurb for Why I Write About Elves by Terry Brooks, but I assume that one could be summarized as, “‘Cuz they sell.”

SF Signal has the whole list.