I've been wondering this for a while. Is it because the few Steampunkish films released have done really poorly, like the Wild Wild West, and Sky Captain and the World of Tomorrow, or because Hollywood just hasn't caught on to how cool a well articulated Steampunk film could be?
Bloodrunsclear created this fake Weird West movie trailer by chopping up other films.
He did another fake trailer for the movie version of Leviathan.
And, I had to pick one actual steampunk movie. Here's the steamboy trailer.