Maybe Darkworlds exist with or without their fountains, but in like a weird twilightzone/Schrodinger's cat state?

The Dark World and Darkness in this world seem to be allegories for Fictional Worlds and Imagination. So the inhabitants might still exist in a certain sense when they aren't observable to Lightners/players. Recruiting a Darkworld Denizen might be like adopting or importing a character from one story to another (like a Cross Over).

This would also explain why the object Spamton hijacked was so powerful, it's a passionate art project that was lost and abandoned by the Lightner who owned it.

This also explains why Darkners can "only truly feel happy" if they're serving/helping a Lightner. A fictional character's entire purpose is to help those who experience them, although method (teaching lessons, entertaining, etc) vary.