I enjoy it so much that I'll spend months, years, developing worlds for RPs before I even release them. If I even get to that point.
That sense of power... the ability to shape and organize a world exactly to your liking... and sometimes, not to your liking to create a better story and conflict... it's such a rush. Coming up with even the littlest of things is fun. And if I'm not good at a certain aspect, I just hand it over to my bud and he makes it better for me. (Like maps or scientific-type things) So it just gets even more fun. Working with someone else and discussing how to create a world is really one of the most exhilarating experiences I have ever felt. Especially if you can weave your ideas in and out with that other person, and create brilliance. I really cannot emphasize how alive it makes me feel. I enjoy it so much. When I create RPs, I also encourage people to shape my world together with me because of how much I love collaboration like that. It's a shame they're often hesitant and afraid to do so out of fear of breaking my plans or the stories.
World building though, it is hard work, and I can only concentrate my attention on crafting one world at a time. I've been working on that one world for years. Anything else is a small side project that I can't really give too much attention to. For things outside of this world and concept, I prefer to go with others' ideas and let them take me along for the ride. Their interpretations of Pokemon or even original content give me more variety and can even be inspiring to my own thoughts.
If you're curious though, I have designed my own Pokemon region in conjunction with my map-mapping buddy, Mr. Lunaris Adamantine. For an RP concept that we've kind of scrapped for now.
This is the map. He made it; I just colored it. This region is unique in that there are technically no Pokemon on it... at least the surface. Pokemon training is illegal, and all Pokemon are actually humans who have been punished for committing various crimes forced to work underground as slave labor.