If you aren't a known developer, people want to see some evidence that you have the ability to make good on your plans. Game development isn't simple, and many people are not prepared for what they are going to have to do to bring a successful game to market.
So Doublefine or inXile can get a good bit of funding with nothing but a design doc for a game because people have faith they'll be able to deliver since they are experienced game devs. New crews are going to have to show something to get people to trust them.
Particularly in light of past KS failures in that regard. I've backed a number of games on KS and two of them I knew were fairly high risk: They were being done by an individual who hadn't done a game before, and there wasn't any sort of demo up front, just some basic concepts. I decided to take a risk on it, but fully understood that failure was likely.
Sure enough, both are floundering/failing. One hasn't had any updates in months, the other does update periodically but it is still extremely rudimentary, despite being way past the planned launch date, and it is pretty clear the dev just doesn't have a good idea how to proceed from here.
On the flip side, the games by established studios have either delivered or are well on track (Shadowrun Returns was brilliant, Wasteland 2 ships next Friday, Pillars of Eternity is in beta, etc). Likewise the indy titles that had a demo and were a good bit along with development have delivered, like FTL.
So no surprise many people aren't willing to take the risk. They want a better chance of return so they stick with established devs or with things that have some proof.