Describing what joy brings to any activity is like trying to answer, "Why Jell-o shots?" "Who would do Parkour?" or "What happened to the undercarriage of your grandfather's car?"
That is, you can answer, but you can never really explain. And like many another, it's a quality easily identifiable at ten paces.
As an illustration, take a look at this strangely joyless rendition of the goofiest, happiest of dances:
This flying lawnmower (yes, I know this video has been around for ages. And yes, I understand how they did it. Don't be a buzzkill, bro) on the other hand, is utterly joyous: