I feel your pain Fiji. I know your frustration. I have asked myself the questions you raise. It's why I only watch series that have concluded, and whose stories hold together well. I will NOT waste my time on TV where the writers appear to be winging it.
TV writers complain that they're on the bottom of the pile when it comes to TV fame and fortune, but I would guess that they're paid damned well to do what they do. For so many of them to do what they do so poorly is inexcusable. If I were biblegod, the first level of hell would be for lazy, contemptuous tv writers, with the duration of punishment to equal the amount of time they spent pooping out their crap scripts.
I believe that such writers think that their viewers either don't care or are too stupid to notice.
Then you have the heroes... the one's that write well, who care about their product or even their art and have respect for their audience, like those that write for Breaking Bad, Mad Men, Justified, Orphan Black, The Killing, Foyles War, Sons of Anarchy, The Thick of It, The Wire, Babylon 5 (4 seasons) IT Crowd, Better Off Ted and so many more. Good programs that do not violate their own internal logic. Some are serious and even depressing dramas, some are lighter and others are comedy, but they all do a fine job.
Don't get me started on the way Alias went from great to dreadful, or the way Ugly Betty went from enjoyable to dreadful. And let's not talk about the movie Prometheus... Dreadful!