That's only because cars are by far the largest share of transportation period.

When you normalize by looking at the death rate per person-mile, the numbers are very different. If you're trying to decide "what is the safest way to get to work", then the best numbers I could cobble together (which are not great) from a few sources are:

Deaths per 100 million miles:

    Car:        ~1
    Bicycle:    ~9
    Walking:   ~16
    Motocycle: ~40

Really, there are two different questions to ask:

1. What is the safest way for me to get to work?

2. What is the safest way for all of us to get to work?

You might assume those have the same answer, but they don't. The safest way for all of us to get to work is probably to have everyone walk and/or bike. But if you unilaterally decide to start biking or walking to work in a heavily car-dominated area, you are increasing your own personal risk unless you can find a route that separates you from the cars well.

Transportation safety is fiendishly complex and no one sentence comment on HN will capture it well.