Six months is plenty of time for a media blitz. Getting the press releases & stuff out to all the web sites & gaming magazines at the start and then keeping them updated is a job in itself.
If you start the flood at the right time, everyone knows it's coming and will be expecting it when it arrives; too soon and they get bored reading about it and cease to care.
The idea of any marketing campaign is to grab and hold interest long enough to guarantee high sales. For a small and relatively unknown company that window is much smaller than for one of the big players.
Also, a small company has to take people away from one thing to do something else, so the more time the Larians spend talking to us, the less time they have to work on the game, so the slower the development work goes.
My guess is that the Larians don't feel they have any really significant developments to report, yet. More screenshots would just be a tease, and likely result in a lot more requests for info they aren't ready to share yet.
This is why I don't mind waiting. I'd rather get good info when they have it than the odd teaser released just to show us they're still here.
