Impatience
Drivers regularly do the same, even accelerate whilst crossing amber lights.

not sure but don't you think their life is more important than losing the ten seconds it would take for you to stop and not run them over?

They're all impatient and sometimes they think they can beat the car.

Suicidal bid

Pedestrians hate cars, and drivers hate pedestrians.
As humans we tend to take the path of least resistance. With no one enforcing "jay walking" laws, it makes it "convenient" to cross at the shortest pathway across the street.
Unfortunately, the pedestrian has the right of way and so when we are driving we have to abide by these laws. Besides, how would you feel if you hit a pedestrian/cyclist/skateboarder?
At traffic lights, some pedestrians will just wander across the road as long as it appears to be clear. Some are wearing i-pod ear buds, some are talking on cell phones and thus distracted from their own zone of safety.
I guess we can't get too self-righteous because we ALL make little errors and omissions daily, don't we?

Because they are using the Queen's highway. They can do this without licence, tax or insurance, quite legally. The lights, road traffic rules and all the other restrictions apply to vehicles.
Oh and yes I do drive.