Writing at SciFiNow, James Rundle points the finger for the show’s declining ratings at the Stargate fanbase:

Perhaps a more seedy, and disappointing aspect of the hits to Universe’s popularity, though, is the fanbase itself. “I don’t think if we for any reason go away, it is an issue necessarily of the quality of the product that we’ve been making,” said executive producer and co-creator Brad Wright. “I think getting moved on the schedule has hurt us. And the fact that some of the fans that liked SG-1 and Atlantis were so angry that they have deliberately hurt us, which is unfortunate.”

I’m going to go out on a limb and say that the main problem with SG:U is that it’s a Stargate show.

I actually really like the series. While I thought it got off to a bit of a rocky the first ten episodes or so, they closed out the first season strongly. If anything, the show has gotten even better in the second season. However, I’m not a Stargate fan. I gave up 3 episode into SG-1, have never been able to sit through more than a few minutes of Atlantis, and never bothered with any of the other miscellaneous entries in the franchise.

Meanwhile, judging by the comments I see following any article or review referencing SG:U, Stargate fans hate the show— it’s too much like BSG, there’s no humor, there’s not enough MacGyver/random-alien-they-all-love/whatever. In fact, the thread following Rundle’s column provides a fairly representative sampling.

So that leaves the show in a bit of a bind—the traditional fanbase thinks it sucks because it’s not like the other crappy series that they love. At the same time, it’s still got “Stargate” in the title, so by and large, everyone else is going to write it off.