This phenomenon arises from the way that TV shows are produced. The creators write ~6 episodes to showcase the concept and the funding/production decision is made based on these 6 episodes. So the shows are engineered for maximum drama during these 6 episodes, and the rest of the show’s run is trying to maintain a 100 meter sprint pace for sometimes up to 10 years.
This is particularly bad for “conspiracy” type shows where the protagonist uncovered some massive conspiracy in the first six episodes. The rest of the show usually ends up escalating the conspiracy to the massively absurd. “Oh this goes way above the President... it’s a shadowy cabal with an underground lair in Biarritz that is manipulating the entire world for... reasons.”
Out of all the shows in this vein that I've seen, Person of Interest was the only one that managed to maintain its pacing.
The key seems to be recognizing the season-long and multi-season arcs, making them both satisfying, but never getting to an "Oh, what do we do next?" point.
Well, it and of course Babylon 5.
And maybe Lost. I know it gets nerd hate, but I respect it from a show-running perspective.
This is particularly bad for “conspiracy” type shows where the protagonist uncovered some massive conspiracy in the first six episodes. The rest of the show usually ends up escalating the conspiracy to the massively absurd. “Oh this goes way above the President... it’s a shadowy cabal with an underground lair in Biarritz that is manipulating the entire world for... reasons.”