I am a writer. I have written software manuals, insurance presentations, tests, letters, resumes, memos, poems, stories, novels, articles, interviews, and more. I have edited and proofread countless textbooks, journals, and other things. At no point in my life have I ever made more than $30,000 a year. The competition to get published is akin to jumping into a pool infested with sharks. Once you're published, reviewers and critics can punch a hole in your work and watch you sink to the bottom, all the while congratulating themselves on how cleverly they did so. At the end of the day, any non-writer you tell about your job thinks he or she can do it better with no arts education and a complete disinterest in reading. Everyone I tell about my poetry is also a poet; even that woman down the street who "jots a bit in her journal now and again" has been published by Poetry.com.
There are only two reasons writers keep writing. One is because we love creating something with words. The other is the hope that someday we will be in that top .05% of writers that makes the bestseller list (think J.K. Rowling or Dan Brown) and rakes in a ton of cash. Most of us will die before that happens.
This is why we like booze (and chocolate) so much.
(edited to add: I stopped working full-time when I had my two kids, just fyi)
(edited again to add: I should probably mention how cool it is to play with words. Seriously. Writing a perfect poem is one of the most sublime experiences I've ever had. So, while all that up there is still true, I should have explained more about the "we love creating something with words" part. Just sayin'.)