I live only a mile and a half from the school where I teach, but I would never consider biking. Only one route exists for my short commute, and it's narrow roads with heavy traffic (and crossing a large intersection). Add in that for at least half the year I drive in before the sun's up. Also, I must dress professionally, and I don't want to change before my 7:00 classes, plus I'd have no safe place to store a bike at school. Finally, if I were biking, I'd be sharing the road with high school students, who are often more focused on friends, music, and breakfast than on their driving.
My conclusion: Biking may be a great option for some people, but it isn't something that'd work for my circumstances. I'm not going to beat myself up about that.