How many themed communities have you seen out there? How many were inspired by 30_kisses or fanfic100? Now there's one solely for Law & Order (plus Conviction). Four prompt tables of twenty-five themes. All themes are titles from Law & Order, SVU, CI, TBJ, and Conviction.
30_kisses and fanfic100 are fanfic themed communities. Most fic themed communities are started by people who saw/participated in at least one of them. Then, they wanted to tweak the rules a bit or change the focus. When they made their own fic themed comm, since they did not come up with the idea on their own, they credit the community(ies) from which they stole the idea. When they credit, they usually say "inspired by 30_kisses" or "inspired by fanfic100." That's where that came from.
Both communities cover all fandoms, and there are many others that cover all fandoms and a few that cover one specific fandom (i.e. Harry Potter). 25_crimes is the first (to my knowledge) that covers only Law & Order and Conviction.