Why don't motorists take the right-of-way when they have it?

So you're on your bike, and you're coming to a stop sign. So you stop, because that is your duty as a vehicle-type thing. There is a car coming from your right, and heading straight on. It has reached the intersection before you. It has stopped. And then, for no reason in the world, except for some misbegotten sense of magnanimity, the driver waves you on.

In some ways, this is sort of cute. In some situations, it really is just nice. But if you're on an incline, this just wastes the motorist's time and makes you look like a moron as you start trying to go uphill from a dead stop. You can feel them chuckling at your wobbly, desperately pedalling frame.

None of this is necessary. All I'm asking is that motorists take the right-of-way when they have it, and not when they don't. Everything would be better. I would not risk my life, and I would not be embarrassed. Is there something inherently unreasonable about this?

(Yes, I have a lot of cycling rage. It's spilling over into other parts of my life. You can ask my friends about a pedestrian incident in Chicago.)