Why do these guys have more finished Advertisements than developed game content?
Advertisements for a game that isn't even 10% finished, what the hell.
Theres already a couple of perfectly valid replies on this, but theres one (of the 2 main reasons, the other being publicity) which has been missed out, and thats the 'educational' aspect of it. They're essentially using this to learn what tools they have, and what they dont, to be able to tell the stories they want to put across to the end user.
Its like building a film studio from scratch, you dont complete it then decide to make The Godfather or Casablanca, you take the time to get a feel for it, address any issue you might have, and then you bring in the stars and director to make your masterpiece.
Thats the main reason CIG have given, its allowing them to be creative and feel out the tools they've created, and they're releasing it because the backers are excited to see this sort of stuff, and it brings a wider audience because people will see it on gaming sites, facebook, stuff like that, and thats of huge benefit to them funding. The community is also not shy when it comes to criticism, and valid & well argued criticism well help them when it comes to creating the cinematics for SQ42 plus bits in the PU (in-game news reports for example, SP DLC too).
Can anyone name a medium to AAA budget game which didnt promote itself while its being developed? Its all part of the game making machine, but dont discount the fact that dev teams learn from this stuff, especially when they're building so much of it themselves. They need to get used to creating content that feels real, not hollywood blockbuster trailers with funky music and big action clips. This is them working.