At best it would have to be flagged for review, at which point someone would have to check it somehow. Otherwise you'd end up deleting a bunch of totally fine roads that simply aren't frequently used by people who send their locations to Google.
I would also be surprised if every single road in the world has seen usage in the past decade. I'm sure there's a whole bunch of roads that just aren't ever used any more. Doesn't mean they won't be useful in the future. Doesn't mean they should be removed from maps.
Implementing your suggested algorithm would probably make the map less accurate, not more accurate.
Can not have surveillance capitalism without the liability.. Have your cake and eat it. The family is right to sue apple and Google.. If you saw, and you could have known, being a beeping Tom as buisness model makes you liable.