To employ a seasonal paraphrase, "Why are writers different from all other artists?".
The question begs the opposite - "and how are they similar?". Musicians and visual artists (the ones for whom the term"artist" was once to me the only appropriate use of the word) seem to have a different relationship with their output. I read writers constant bitching that the one script they've managed to complete, and which is more often than not a polished first draft, isn't setting the world on fire or filling their bank account. I can't imagine a musician or painter considering a single example of their art as the one defining achievement they rest their futures upon.
Of all the creative dabblers, painters have the easiest access to an audience in the form of the community art show. My town hall has one and the stuff is uniformly crap. Perhaps one in a thousand will do the necessary continuous study and repeated work to elevate themselves to the next level - the selective local art gallery and then -?
Musicians might slip in an original song during a set of Dave Mathews staples and classic rock retreads but they too at least have some possibility of an audience. I know painters and musicians and it's never been my experience to meet one who played me one song or showed me one drawing or painting and had the attitude "where's the recognition based on this one thing".
Maybe it's because the only audience available to a beginning writer is either the internet echo chamber or Mom. Hey, writers, it may be the 10th script or the 20th or it may never happen. But it sure as heck ain't going to happen after 1. Get comfortable with the reality that it's a long haul. You might get lucky, and isn't that what American Idol is all about? The overnight sensation? But it's a lot more likely that tomorrow's superstars are driving around in a dangerously unroad-worthy van play a series of one-nighter's in dive bars.
Let the hating begin!
Your sometimes pal, ROger