I would guess that people read them for the same reason they read National Enquirer or Star, or watch E!, Entertainment Tonight or other shows of that ilk -- pure, morbid curiosity. Why were people fascinated by the two O.J.Simpson trials, and why did Janet Jackson's breast set a record for number of Internet searches? There's just something about celebrities that makes them inherently interesting to most people.

My sister and I wrote some Star Trek fan fiction, and there's a lot of creativity involved. She invented a world, three races and a social history while I contributed a recent history, timeline, integration with the previously established 'official' history (which now appears to be subject to change without notice) and four major characters. The 'name' characters were only background figures and cameos for us, and we didn't use the Enterprise, though we did make much use of Lt. Saavik and Star Fleet Academy. I expect that anyone who tried to write a story set in Middle Earth would also find that only the framework was useful and most of the heavy lifting was still to be done.

Some people find some aspects of writing easier than others. Names (of characters, countries, whatever) and titles (of books or chapters) come very hard for me, and plots are difficult, too. What's easy is creating characters and their backstory and developing the history/culture of a world. Once I have that, though, there's no story! Where's the conflict? How does the conflict resolve without the adventure being a walkover for the heroes? I'm being browbeaten to complete a story for posting in the Library, and I'm tempted to call it "Five Characters In Search Of A Story" for just those reasons.

Naturally, therefore, I don't think that writing an UNPAID story using previously created characters or real people is parasitic, nor does it necessarily demonstrate a lack of creativity (which I note that you never claimed). Of course, such stories MAY be uncreative, just as any other story might be derivative (lex ludite's pet peeve), or simply boring or badly written. Really, is someone who steals characters any less virtuous than someone who steals/recycles plots? Not everyone can be Isaac Asimov.

Last point, this post: If you have little respect for authors who don't bother to create their own characters, what about authors who don't bother to create their own worlds? Setting stories on Earth seems like a horrible cheat to me, but the few who do create 'alternate universes' usually do a horrible job at it and create something illogical or unbelievable. And what about the ones who don't create their own languages? (I've done it, and it's a bitch!) And what about the ones who don't create their own rules for how gravity and baryon numbers operate? I mean, not inventing alternatives to the nuclear strong and weak forces is just unforgivable. To co-opt something so fundamental must be the height of laziness!

Tch, tch. There're parasites everywhere these days.