Actually quite the opposite, we have a large number of talented writers and artists on here, they just choose not to write fan fiction. Why you ask? Easy, fan fiction is not about being creative, fan fiction by its very nature is not creative, it is taking another persons work and adding your own story or spin to it. The majority of fan fiction simply relies on premade characters, settings, ships, universes, etc... then adds a new story to it. That is not true creativity, especially since most it, well it just stinks. I have read a fair amount of fan fiction and most of it falls into the following catagories: Fan boy wet dreams (ex: vader vs maul fight), fan boy sex dreams (ex: Misa and Minmay get drunk one night...), fan boy backlash (ex: vader's emo diary's), superships (ex: a reborn Kahn builds a 2000km long super mega ultra DY-15,000,000 to kill the federation), cross overs (ex: SW vs ST, et al), side stories aka this one time in an RPG (ex: a rebel gets caught behind enemy lines and must fight his way free). For the most part these are not well written but every once in a while a diamond in the rough comes out that is actually worth reading, if only because the writer doesn't take themselves or the subject too seriously and writes something funny.
Of course I chalk a lot of EU type books up to this too, but at least in those cases the books are for the most part well written and include some new and interesting characters. Heck take say a Zahn SW book, change the character's names and it's no longer a SW book with a little revision, which makes it good.