"People do not migrate, even in today's crowded world, simply because there are too many at home. Crowding would be called a 'push' factor by modern demographers, a negative condition at home. But there are other kinds of 'push' factors - war, disease, crop failure, climate change, institutionalized raiding for loot, high bride-prices, the laws of primogeniture, religious intolerance, banishment, humiliation, or simple annoyance with the neighbours." (David W. Anthony, "The Horse, the Wheel and Language")

That's a lot like Hay River, you see. Crop failure (crappy economy), high bride-prices (no one to date) and considerable "simple annoyance with the neighbours."