Legend Films/Rifftrax turned Rick Sloane down.
Interesting. I wonder if it was because of the knowingly bad nature of the movie. Now that they've done Sharknado 1 and 2 (and are presumably likely to do 3), maybe they have softened their stance on such things.
Or maybe the only reason they did Sharknado at all was just because it was a bad movie cultural zeitgeist that Rifftrax knew they could take advantage of.
EDIT: Grug beat me to it by a few seonds