Aside from lack of time,talent and inclination that is...
Writers and Financial Woes: What’s Going On « Whatever
Writing takes a lot of time, if you aren't able to sit down and write for relatively long stretches of time, you're not going to get anything done. Most writers don't really ever get compensated for the time they spend actually doing the work. I say most, because obviously some do, but again, most people who would want to write for a living do the cost/benefit and end up thinking that a good job and a healthy marriage are more important than spending every free moment for a year or so writing a bad novel and having it rejected as not good enough, then doing it again... and again... and again, only to see a rejected A-Team script make it to the top of the NYT bestseller list.
The guy who writes that crap (please God let it be me someday) might make a year's salary all at once, or dribbled out in tiny checks over the next couple until the paperback gets sold or the movie rights. Then he'll get a chunk he can share with his agent and the credit card companies, while the publisher makes a mint and the actor who plays the lead in the movie version gets 10 million for six weeks of work.
Meanwhile, you're still selling comic books, blogads or rare fish over the internet. While your wife works her ass to the bone at some soulless office job for health insurance and so you can afford your quarterly Apple upgrades, your Netflix habit and all that writerly bullshit you bought into, like the high-end whole house sound system, the taste for expensive Scotch, fine pens and LL Bean outerwear. Not to mention trips to Whole Foods for organic, free range otter penis chips for the wine tasting you're hosting. But don't worry, she still remembers how hard you worked on that 700 word piece you sold to snark.com for $25 bucks in 2004. Seriously, she has it printed out in the office, and everyone thinks it's really clever to compare the shows "Quantum Leap" and "Enterprise" with America pre- and post 9/11.
Anyway. To the 10 reasons listed by Mr. Scalzi, we could add that lots of people who write "for a living" don't really, and even more of them write stuff that no one wants to read, add to that a taste for the finer things and an inflated sense of self-worth and, well, you get a writer in financial difficulty.
You'll see this a lot with musicians, teachers, non-tenured professors and stage actors too.
Crusty old blocked bloggers who have a porchful of kids with crooked teeth know exactly what they're worth.