We can save them a lot of trouble. The answer is simple, really: It was because the person who was struck was riding a bicycle at the time.
If the person had been a pedestrian or driver of a car, the bus driver would have stopped, especially with passengers hollering at him.
We all know that. It’s just a given in our society.
For someone riding a bike, though, the rules are completely different.
So think about what that simple juxtaposition implies, and ask yourself why.