NAT Tracks
If you look at great circle routings they all take you rather far north if your starting point is in most of Europe, hence the NAT tracks. The tracks are adjusted every day to optimize for wind and weather. You can also fly off the tracks. If you are in a plane capable of flying above FL 430 you never need to go into the track system at all.
If you are going from Madrid to Miami you probably stay well south of the tracks on most days.