First of all, a movie like this seems right up the Coen Brothers' alley. And secondly, they haven't written anything that they didn't consequently direct since Crimewave in 1985.
From what I have read, they had the Gambit script done shortly after they finished No Country For Old Men. Does anyone know why they are unwilling to direct Gambit?
according to an interview, the coens wrote many scripts back in the day just as assignments from studios, probably to pay the bills. or, they were interested.
anyway, 'gambit' was a script they wrote 10 years ago, one of the many they wrote on assignment that never got made. then, a couple years ago, someone decided they wanted to make a remake of gambit, learned the coens had already written a script, and decided to brush the dust off of it, buy the script and make it.
i guess they just wanted to make the movie, didn't feel like asking the coens? not that the coens cared either.