Choice. I could afford a car, insurance, repairs, gas. But why? And taking the bus easily adds an extra hour to my work day over riding a bike. So I bike most days, and when my knee is bothering me, I split commute, loading my bike on the bus rack. This allows me to skip the first bus altogether, and not have to worry about making a transfer. Doing this adds about 10 minutes to my commute over biking alone.

Edit: Actually... I have a truck. I just haven't finished fixing it. The tags are paid for the next 4 years, no payments, and I don't have insurance on it, so it's not costing me anything, and I can have it fixed and drivable in a week if it's necessary.