i think i know where your going with this thread but therefor nobody has taken into consideration:
it takes them 'X' amount of time to fix and sort every game mode out and maybe they are working on the survival just as the previews are about to be released
Not just survival but maybe they don't want so much information or anything to be taken into consideration we all know people go round moaning and complaining because one game cant suit everybody so they just showing survival footage to slacken the tweets on twitter or of some sort.

Meaning... they are just persuading you with survival keep your mind occupied on it and thinking arr it looks sweet i cant wait for it to be released all this and the rest but therefore if you think about it you saying that keeps them slack and sweet without no pressure its early stages anyway so there is more time for more game modes and such to be shown as previews...

they are paying attention yo multiplayer there only doing this to hype you up and wanting to know about multiplayer so you get intrested