> I've always been baffled by why Google search — the flagship product by the world's largest tech company — has so many totally undocumented features.

If I can speculate on their overall behavior, there's no intent behind this. They are relatively decentralized, and everyone is throwing stuff at the wall and seeing what sticks.

To have a feature known you need concerted effort by design teams to make it accessible, marketing to make it known and so on. There's nothing of the sort with Google.