Why All Planes Take This Overcrowded Path Across The Atlantic Ocean

On an average summer night, around 1,500 flights traverse the Atlantic from the United States to Europe. And almost all take this one route – like a highway at rush hour. These planes are separated by only 40 miles in distance and 25 miles laterally. Vertically, they fly as close as 1,000 feet to each other. But why would all these planes take one route when they have the whole sky – especially when that route is becoming more and more dangerous?