The problem is the way Maps determines routes makes a lot of assumptions but there’s rarely, if ever, a human to correct it until it gets reported a significant number of times. It also tends to fine-tune the routes based on data from drivers. If enough drivers drive down a road and onto another road with Maps open, Google takes that to mean the road is open and the route connects.

In these kind of backwater, low population places, there often isn’t enough data. Not enough people driving down these roads with Maps open, and not enough people that encounter a bad route bother to report it to Google. So no human ever corrects it.

Yet another example of how terrible Google makes its services by refusing to hire humans to manage these things.