Part of the reason is writers and actors have simply outpriced themselves.
The market is flooded and writers are demanding more profits. And it's not just Hollywood it's everything. Look at sports till the mid 80s, most athletes, in football, baseball or basketball etc, who had great careers could at best hope to own a resturant or bar that would be successful because of their name.
Now all but the most mediocre pro athletes can make millions and retire.
In the mid 80s writers on top ten series were pulling in half million dollars or more per year. But Hollywood disguises this fact by lumping all writers together, even the ones that don't ever sell anything. Thus the average is next to nothing.
Writers like on "I Love Lucy," were comfortable, quite comfortable, but they still HAD to work and they kept working well into their 70s.
Reality shows are cheap and talent is basically free. They are cash cows.
Add to this a glut of great past shows. I am a fan of old time radio and I am astonished just how well written those shows are. They have to be cause they can't rely on sight.
So why write something new when I can listen to the old stuff already out there?
Then we the TV viewer are sold things like HDTV. Sorry but outside of sports and a few nature shows, High Def is worthless, I mean Seinfeld is no funnier if it's clearer. And that is if anybody bothers to spend the money to convert the show.
Go to books on tape, as I am writing this I am listening to Donald E Westlake's books on tape. His Dortmunder series is hillarious and is far better than any TV show.
Times change, like Rock and Roll killed Tin Pan Alley and R&B killed of Rock and Roll.
Reality killed of most scripted shows, but in a way it's kind of a return to the Vaudeville days of the early 1900s when anyone with any talent no matter how marginal was given a chance to show what talent or what little talent he had