I've never contracted, but I'm in the exact same boat with regards to being someone else's full-time employee. Lately I've been struggling to stay even one year—I've been with 4 companies over the past 4 years! I'm a "flight risk". :)
And it's not that I don't want to work. I put 3-4 hours per weeknight into side projects, and another 8-12 hours on weekends. I have yet to make money on the side, but I keep hoping that something will succeed and I can run my own ship.
Perhaps you feel like you're chained in when you're working for an employer - I feel like it's a gilded cage. Yes, there's healthcare benefits, dental cover, bonus if I'm lucky, that kind of thing but at the end of the day I'm owned. My time is owned, my attention is owned and although I can pull the red cord and quit it's essentially bondage. Quitting becomes harder to do when you have a mortgage and kids, too. So you put up with it, and make yourself miserable, or put up with the misery.
But start working for yourself and all that goes away. You have CONTROL back - you dictate what you do, i.e. what you find interesting. Of course, the difficulty is making enough money to live, and finding that balance. I can't make money from side projects, I'm not that talented, but I can make money picking and choosing the projects that suit my interests and contracting is a happy medium.
And it's not that I don't want to work. I put 3-4 hours per weeknight into side projects, and another 8-12 hours on weekends. I have yet to make money on the side, but I keep hoping that something will succeed and I can run my own ship.