Walking is slow. Walking a mile takes around 20 minutes. If you walk a mile to the transit station at the beginning and walk a mile at the end, that's 40 minutes of travel time before you even factor in the bus/train trip.

Of course, walking is to be encouraged where practical, but it has a very short effective range compared to a bike or scooter. Scooters and bikes drastically extend the effective reach of transit stations, with much less of a downside compared to cars (less polluting, less noisy, less danger for others, less parking space).