I could say the majority of the blame (the percentage is unknown) can be placed on the Producers, other ones include MGM for not keeping a tighter look and Syfy for well, agreeing to that stupid 2 year contact, but also the two of them combined for not shutting the mouths of Producers/Writers/Actors mouths in their little arrogant based rants, unless they were giving enough rope to hang themselves, unsure of that.
Looking back (and this is my opinion) but Stargate was dying in season 8 of SG1, creatively they were running out of ideas despite having an awesome vehicle in science fiction to create new and interesting stories. When SGA came around (a show which I will admit I'm not a fan of) was supposed to be a fresh slate, start a new, trapped in another galaxy, new enemies new technologies. Sound familiar? SGA was the half way point of the end cycle, keep in mind, this is talking about the creative side/process not the audience ratings. SGA was a show that was sustained by the actors/actresses, however when they were gone, SGU came around the writing/producing talent was exposed with nothing to hide behind. Just my opinion.