Missing the obvious

So here's a question that, it's said, American pre-schoolers managed to answer correctly. I didn't, and I'd love to find some kids to try it out on to see if they really see the answer so easily.

"In which direction is the bus pictured below travelling?"

Any idea?

The answer the children gave was: "left. Because you can't see the door".

Now why didn't I think of that?

Credit: Datrio