That's the nice thing about the freedom of choice on this site. Those who enjoy fandoms can write fandoms, while those who prefer to create their own worlds can do that too. Fandoms might outweigh "original" content, but it isn't like original stuff doesn't exist. Similar to Penny, I've got 7 ongoing 1x1 RPs that are all fully original in the sense that my partners and I built the worlds, ourselves. You can find topics that interest you if you look hard enough - or make the thread.