I also love the world building, but I think I approach it from a different direction. Rather than prepping sessions, I like to build mechanics and details into the world. These are often informed by the actions of my players, but in the game it allows me to run a similar “zero-prep” style because the world already exists. Especially after several campaigns in the same world, when so much has been generated over hours of play.
The experience of seeing my world unfold before me, and seeing the wonder and emotion on my player’s faces, brings me so much genuine joy. I feel like I did when I was a kid.