That's the reason right there, and there's nothing wrong with that. We tune into these shows to see the dinosaurs and the aliens and the zombies because those are the fascinating elements. Drama can be had on any channel on TV but these specific elements cannot. Obviously since we're talking about TV shows which have a lot of time to fill they need to show interpersonal drama in relation to those specific genre elements. But the problem infecting all these productions now is that they emphasize the drama (which we can get anywhere, yawn) over the elements that draw us in in the first place.
Shows like The Walking Dead try to head off any criticism of the drama by claiming that the show is about humans living out their lives with the zombie aspect as the background, but not the main focus. That's fraudulent as the creators damn well know people only tune in for the zombie aspect. Same with Terra Nova and the dinosaur aspect. Same with all these shows. It's a con game that viewers are wise to now. The demise of SGU proves that people had woken up to the fact that they were being scammed.
This is BRILLIANT!
The "younger, dumber" audience is still a holy grail they want and its just not going to work. The brain gets bored easily when it is being subjected to vapid, repetitive tasks or images or sounds. Anybody who owns fish and is around the tank daily can tell you that they can "no longer hear it" unless they think about it or it is turned off. The brain's "intellectual spam filter" is just a decriptive way to say it.
We all have this filter, but for most of us it is operating in standard mode (unattended). I have mine in advanced mode, with the cynicism sensitivity up a couple of ticks. Too many false starts, misleading trailers and promosing press releases, followed by the same old garbage wrapped in a different package. Just like you said.
We tune into these shows to see the dinosaurs and the aliens and the zombies because those are the fascinating elements. Drama can be had on any channel on TV but these specific elements cannot.
If the "fascinating elements" are the trademark of any show, why not serve us HUGE dollops of it every week without the soap? I think maybe it also has to do with the writers themselves. How can they write good science fiction or fantasy or horror if they are overshadowed by the drama writers? Perhaps there is an unseen hierarchy which takes truly good ideas and then runs them through writing teams, and along the way they pick up morals, politics, fads, trends, product placements, etc. What comes out of that is the garbage they are releasing these days. Trying to be all things to all people and ending up being a two-headed freak that appeals to nobody.
The Andromeda Strain of 2008 was a PERFECT example. The original of 1971 was such pure science fiction (MUCH more science than fiction), it could have been classified as a dramatic factual documentary. It was a dramatic portrayal of an actual biohazard protocol and a "theoretical" biolab which could contain or deal with the alien microbe scenario. The actual military and other official entities get credits in the movie. But then the 2008 version had several additional layers of lame drama, relationships, betrayals, and a sinister plot behind the solution. LAME. They ruined it. But they used the "fascinating element" of the original movie to draw people in.
People only allow a bait and switch once or twice before they arent so dumb anymore.
I've got to remember that one. 
It doesn' matter if it is a different channel- it's all groupthink all the time in the entertainment industry! 
they don't have an original idea left I swear!