That’s the way it is in every genre of television and movie. Who’s the it person, what’s the latest look and hottest style. And of course sci-fi makers are going to jump on that bandwagon to try to bring it into the mainstream. Eye candy is great, but acting ability should factor into it somewhere, even if its the rest of the cast.
Sci-fi is a very unique genre, undefinable by most who watch it as evidenced by the discussion here on Sadgeezer.com. Making it mainstream will destroy its uniqueness. On the flip side of that coin, making it too inaccessible to the casual viewer will render it useless and unairable.