Walking is different because you can stop on a dime and dive out of the way if you see trouble coming. On a bicycle, however, you are usually unable to do this.

Walking is different because you can stop on a dime and dive out of the way if you see trouble coming. On a bicycle, however, you are usually unable to do this. Additionally, the increase in speed differential (which is much more significant for cyclists than pedestrians) created by cycling towards oncoming traffic greatly reduces available reaction time of both parties. When you are travelling in the same direction as the traffic there is usually still a speed differential but it is substantially less. While you no longer have the ability to see potential problems "coming at you", drivers have significantly more time to notice you and react accordingly.