A couple things to note.
The game is still very early in development, and most of the major systems aren't in. So there isn't quite as much to show.
There are quite a few clips strewn about the forums, which can often be hard to find. Difficulty finding and keeping track of these kinds of things has been a persistent problem.
The exclusive backers (10k+) do have a bit more information and more access to demonstrations of the development, most of which has not been leaked on you tube.
I think the most likely answer that you will hear from the dev team is that they would have to take time away from development to make videos and they do not have a big team so that would be more detrimental than what other studios may be able to do.