I believe 7 years is the longest a series should be on the air. anything after seven years is wasting the talents involved. I would rather those working on entertainment projects move on to other new creative endeavors.
That's also the length of time The Beatles were together, I always say that they did break up at the perfect time.
I had never thought about it but I think you are right.
I used to like “Smallville” despite it’s obvious PC moments but Season 7 seemed to be the end. It lasted one or two more seasons but I had quit watching by then.
Seven years is about how long I watched The Simpsons after the series debuted. I laughed heartily during every episode. I loved the show.
And then I just stopped watching it and haven't watched it since. It wasn't a conscious decision, a boycott, or anything of the sort. I just stopped watching it.