I read it before, it's pretty good.Neil Gaiman's? It was A Study in Emerald, which is a fusion of Holmes and of Lovecraft's Cthulhu mythos and set in a timeline where Moriarty's the detective and Holmes is the mastermind and the world is ruled by the Great Old Ones--fish dudes, basically, and old gods. (I think it got turned into a game and a graphic novel at some point? But I know it got a Hugo award back in 2004.)
to answer your question, I'd say it's a legal issue- Who hold's the copyright/license etc?