From Brian J Smith, who was asked about SGU's demise:
The economics fell through and the ratings sucked big time. You can point fingers and you can blame whoever you want, but the ratings were not there. Stargate Universe was one of the most expensive TV series to shoot on television, period. There are shows out there that get 20 million viewers a night that shoot for a fraction of what it cost for us to make a single episode of our show. It makes no sense to be spending that kind of money on a show.
Rest of interview here: