So any time you have a bunch of long, flexible objects (or, in the garden hose scenario, one really long object in multiple loops), the objects link in a number of places. When there's enough contact points, and the objects are long and slim enough, the chances for these objects not getting into one of those trillions of knot states is downright astronomical. The more contact points, the more possible knotted states.
At some point, it's just easier to use a bowie knife and buy a shitload of cords.
So even a little motion -- jostling the box of Christmas lights when you move it, a change in temperature causing your garden hose to shrink a tiny bit -- makes those states catastrophically accumulate, often within seconds. Put the headphones in your backpack, walk across campus, boom: You have descended into knot hell.
Can It Be Fixed?
Yes and no.
The actual knotting will happen no matter what. Sure, the crucial element is motion, so restricting that by neatly arranging the cables and securing them with, say, cable clips will do the trick. But if you are the kind of person who considers that an option, chances are your cables are neatly arranged and alphabetized already.
Which is widely considered an early warning sign of sociopathy.