Too many shows and book series go on for too long. Rather than end at an ideal spot to maximize the art/story of it all, they keep going until the creators get bored or the money isn't flowing anymore...
I regularly stop watching a 7 or 8 season show after 2 or 3 seasons. No guilt, got the best from them, don’t owe any more of my time to diminishing returns. It’s very liberating.