The sword has always been a weapon that speaks to the imagination. Where most weapons stem from a practical everyday use, the sword is purely designed for killing people.
The raw materials and the skill to forge them in to a weapon purely meant for killing were awe inspiring even during the days in which swords saw active use. Swords have also played a big role in myths around the world and made mythical figures of warriors proficient with the weapon.
With swords being out of use in most parts of the world and people being so far removed from the very real horror of its use its mythical status has risen even further in popular culture. This status has attracted interest from people in all walks of life.
The longsword is a prime training tool, with the distance and two handed use it is excellent to teach someone the basics of fighting. It also removes any ignorant notions that you can 'take a hit' forcing you to move properly and apply the governing principles. However the saying “easy to learn, hard to master” definitely applies.
The longsword is one of the most featured weapons in the historical manuscripts which give instruction on its use. Because of this prominent appearance in manuscripts, there is simply more information about its use than other weapons.
And let's just be honest here:
Longswords are cool.