Why do pedestrians thank drivers with a wave for stopping at zebra crossings?

Is it because motorists so rarely give way to pedestrians at zebra crossings, let alone side roads?
Or are we so deep into the car culture that pedestrians are grateful not to be mown down by cars every time the go out?

How many drivers thank other drivers for stopping at a give way line?

I can see no difference between a zebra crossing and a give way junction from a vehicle users point of view.