I mean, that's fine if you want to avoid Russia while flying from California to Quebec, but you don't really need an app for that one. Whereas if you're within the plane's fuel supply of where you don't want to be, how are you supposed to know ahead of time what kind of nonsense is going to happen while you're in the air?
The plane could have a navigation failure over the ocean and end up arbitrarily far off course. Some first class VIP could have a medical problem which is going to force the plane to divert anyway and then the nearest city with the right kind of hospital is in the place you don't want to be. And what if you end up St. Petersberg not because you had a layover in Finland but because Helsinki was your intended destination?