Why no Gnomes in any cinematic trailers?

They were there, the camera just... okay, old, sure, but maybe they tried to take the cinematic and apply their own ingenuity to improve it and accidentally deleted themselves in the process? Stranger things have happened.

Anyway, the easiest way to explain it is that we do what we think will be the most awesome. It has nothing to do with any favoritism. The Horde trolls had only a small part in only one of the cinematics and the most recent (WotLK) took a different direction with them that was much more story driven so putting a gnome in there wouldn't have worked. (Just say no to skeletal gnomes).