Follow the money? It's a constant trend; I see them every day flying over my house in Gloucester - that's in Gawcestershire, Englandshire. I shudder to think what all those planes are doing to our atmosphere!
Fascinating graphic, isn't it. You can almost draw the lines of each of the Westbound "NAT Tracks" by the flow of traffic. I suppose on this side of the pond we tend not to be looking at FR24 etc when they are generally flowing the other way in the middle of our night.