Why do all SF and fantasy books grow into series?

I regularly visit the web page of Stockholm’s science fiction bookshop to see what new books are coming out. Even though I haven’t bought any books from them for a few years at least, I go there because they’ve got a very nice overview page where it’s very easy to see at just a glance which new books they are stocking.

The page currently has 30 books; 31 if you count the American and British editions of Terry Goodkind’s Confessor separately. Of the 30, 23 are parts of series – the worst offender is #17 in its series! Two more are associated with series (one is a Star Wars book and one is a prequel to some other book). That leaves just 5 standalone books.

If I want to buy a book, I want a book that is able to stand on its own and is worth reading on its own. I want one book, not seventeen. And I don’t want to jump in the middle of a story. So when I skim that page my eyes skip right over all those series.

I guess series help sell books. If you get someone to buy the first one and the subsequent don’t drop drastically in quality, the reader might keep going out of sheer inertia. But if they missed the first books when those came out, are they going to be interested in book 8? Unlikely, I think. In my case at least series significantly reduce the chance that I’ll even open the book.