lots of reasons... I live on campus now, and am not working this semester, but in the past I rode to save time and money. I worked with a bunch of health-conscious people, many of whom would drive to work in the morning, drive home for dinner, and then drive to the gym to work out for an hour or two. I wanted to stay in shape, loved the open, connected feeling of riding, and didn't want to make exercise into something separated from the rest of my life. Bike commuting was the perfect solution. plus I'm cheap.