I’ve literally watched my car (only car around) trigger the yellow heavy traffic warning (because I was driving slow to look for something).

Yet thousands of cars doing 60 mph through a cornfield and over a river doesn’t trigger a “maybe a freeway was built here?”

Waze was pretty public about how they used it, with automatic flags and route updates with no/little human intervention. I assume everyone else is doing the same, since it's so obvious. I'm sure they know, but if it was a cornfield a couple years before, there's a good chance it's lower on the priority list, in a "how many people will this impact" sense.