In many of the great movies and tv series, why do the bad guys always win in the 2nd to last part?

The producers and writers need to build up for the climax so people will bother to see the last part itself. Viewers aren't gonna let the series end with the bad guys winning, so they'll just have to watch the end! Of course it can be annoying and predictable at times though. Everyone knows the good guys will win, they just have to make sure by seeing the end.