I'd wager that the fact that many high power companies use whiteboards for interviews point to the fact that they're useful.
The fact that there are so many successful fast food chains points to the fact that the food is good and healthy.
This is appealing to authority/popularity.
But since we’ve gone there, many high power companies also have a lot of chuckleheads running around.
Maybe they're only useful when you're a high power company with $200k+ total comp and more applicants than you know what to do with.
Divining rods are trusted by many, and have been in use for centuries. If they weren't a good way of locating water, why would so many people use them?