An author can write one good book of moderate length in a year. Costs for publishing, distribution, and marketing can rack up pretty quickly, but one estimate I’ve heard puts the cost to publisher for an average mass market paperback at $150,000.
Avatar cost between $300 and $500 million depending on who you read; Firefly cost around $2 or $3 million per episode, and a $10 million investment for the pilot (for sets, costumes, developing initial special effects, etc.), and I’ve heard a price tag of $17 million attached to the Battlestar Galactica miniseries.
People invest money looking to make it back, and the more money they invest, if they’re reasonable people, the more they want that investment secured. If I’m sinking $300 million into a really fun movie about pseudo-Native American space smurfs, I want to be positive it will do well, so I become worried when the movie takes risks and breaks ground in its story.I become worried if the story is slow, or doesn’t have an up ending, or pisses off the pro-military crowd without appealing enough to the anti-military crowd. I become worried if the audience isn’t able to cheer with unalloyed joy for someone at the end of the film.
Please don’t think of this as an attack on Avatar; I watched that film and liked it a great deal. But a publisher can afford to put out individual books that take more risks and push more boundaries because there’s less money tied up with each story. In extremity, if you’re DH Lawrence and nobody wants to publish your Lady Chatterly’s Lover, you can self-publish out of pocket these days using sites like lulu.com or createspace.com; by comparison, even a very inexpensive feature film like Rian Johnson’s amazing Brick costs $450,000 and requires the dedication of maybe a hundred people to make it happen. Possible, but well outside many artists’ budget, especially if you’re writing something you feel certain will piss some people off.