They are completely crowd funded, and with how much they have raised (>$200 million), it would be silly for them to sign with a publisher or seek investment. In the beginning they were looking at signing investors, but they raised enough to not need that. Also, with the 2 million people who have already backed the game, they do not need to do traditional advertisements. They do have a presence at game conferences, and produce quite a bit of video about the development of the game as pretty much their only form of advertising.