Why do you do what you do?
Being a self employed programmer I just love the challenge and the fact I earn money all on my own.
When a customer calls me and says "Can you do some software that will do XYZ" - I say yes and then work out how to do it, thats the challenge.
When a customer calls later and says "The software is fantasic and saves me loads of time", thats part of the reward.
When I earn £200 for an hours work, it brings a huge smile to my face. Granted thats not often but it happens.
I couldn't sit in an office 9 to 5 doing similar work each day, it'd drive me crazy with boredom.
Luckily the variety of software I get to do is very wide and I'm learning new skills all the time, so I couldn't ask for more.
So, I do what I do for the challenge, the reward and the money.
*EDIT*
I am tempted to try my hand at puzzle games this year. That'll be something I've never done and if I get a few months of quiet time I'll certainly give it a go.