"Frank Miller is a successful artist/writer combo. So is Paul Pope. Mike Mignola, Jeff Lemire, Bill Watterson, Will Eisner, David Lapham ... the list goes on. And there are a ton of indy artist/writers that also put out a good product, although many will tell you that they don't make a lot of money doing it. So if we know it's possible to be a writer/artists combo, why don't more artists try it?
The truth is that most attempts at being a combo fail. No one wants to be the artist who mills away for years writing (what he thinks will be) his opus, only to have it end up a laughable failure. But I think most of these attempts fail because artists don't respect writing as an individual craft -- rather they think that being in comics for long enough means they've developed writing skills simply through osmosis. Which is bullshit. And it's disrespectful to your medium. Just because you can stand on a hardwood floor doesn't mean you know how to build one."
-- Sean Murphy, laying out his "5 Reasons to Write,"an argument for comic artists to write their own books