It is only like a 50 page supplement that supports the clue gathering GUMSHOE method, cheaper than making a whole new game when there isn't really a need.
Kind of like how you can GUMSHOE cthulhu without having to convert, like having each ten percent be point spend and what not.
I'm sure if there is enough demand for the initial product they might make a whole setting, but they've got soo much already.