They do this crap by spending all their budget on special effects in the first minutes of a pilot episode to hook in sci fi fans then the premise switches to one that needs no special effects.
Continuum did that, they are in the future, go back to present day then are stuck.
Even Star Trek would do that. They start off a season with a few good episodes will of effects, then they go to the holideck and fight nazi's or go back to sherlock holmes days etc. Then for the cliff hanger episode at the end of the season, Borg show up with CGI in tow.