Look, this isn't rocket science - you put out a trailer early on in your marketing that's heavy on cutscenes in order to generate interest and talk so that people are aware your game exists, and once you have that interest you start putting out further trailers that actually show what your game is about. If you throw out a gameplay trailer first (unless it's a visually impressive game, then you can get away with it), there isn't a hook to get regular not-hanging-out-on-a-rpg-forum people interested enough to click and watch long enough to say 'yes, that game looks like it's worth buying'.
If this was their one and only trailer they'll ever release then there'd be reason to complain. Since they literally put the words 'story trailer' in the title of the video, it's not much of a gamble to say there'll be more trailers coming, at least one of which will presumably have the gameplay shown.