Because it has to be repeated again and again: We need to drastically reduce the number of cars to solve our problems.
@AndiPopp so true. My main issue in adopting public transport as a means of travel for work is that most of my work isn't near stations, bus services are infrequent, unreliable and expensive. Also, as a photographer, I carry a lot of equipment.
@timsmalley If your work involves moving between random various places then public transport really is not quite an alternative, sometimes you need to go to a place not even a single bus gets, and that's fine*. But so many people are actually working in offices, and they drive their cars from the place they live in to some random business district in their city, driving up traffic jams along with them. For those people, public transit is definitely an option.

*edit: and an electric vehicle really is your only alternative to reduce pollution in this situation

@AndiPopp