Whether we're talking about TV, films, games, or books, one thing is always true: sequels sell.
When we see something good, we want more of it, but following up on a fantastic first effort can be tricky. This is why terms like "sophomore slump" and "second album syndrome" are so commonly used; making a second instalment of almost anything isn't easy and often results in disappointment.
This is especially true in television. First seasons of TV shows are new, fresh, and exciting, but second seasons can rarely recreate that same sort of magic. In many cases, the writers and directors simply hadn't planned too far ahead and have to cobble together scripts and plotlines in a relatively short amount of time. In other cases, first seasons are just so good and original that their sequels have no chance of matching them.
Whether it was down to changes in the cast, a lack of ideas, boring stories, or something else altogether, these second seasons failed to live up to the promise of their predecessors. In some cases, they even proved fatal to the show as a whole, with reduced ratings ultimately leading to inevitable cancellations.