I worked on Google Maps monetization, and then on Maps itself. Monetization was a dismal failure. I don't know how well they're doing now, but Maps was a gigantic money-loser, forever. I'd be a little surprised if it didn't still lose money, but maybe less. I don't what those "pin ads" cost, but I'd bet it's way less than a search ad. If you don't believe that, that's fine. "What about indirect revenue?" you ask? Goo…
But I think open street maps has a killer feature that Google doesn't have: the community.