From the PDF:
The Crooners come from a dimension of absolutely nothing. No plant-life, no music, no happiness, no fun. They were forced to eat squirmy worms, drink lizard milk, and wear the most horrible furs and skins known to fashion. They were a lesser race of several that lived in their homeworld, Altoos, until they evolved with a simple, melodic squish of worm goo. They began to dance, sing, and perform in the most outrageous of original shows, but this behavior was not well received by the others in the dimension. The more powerful races didn’t comprehend music or what concerts even were and took these these new displays as devices the Crooners were trying to use to overthrow their superiority.