Some have commented on the ongoing list of best TV sitcoms regarding a heavy disposition towards the modern, which I think should be addressed.
When I went over best directors and best actors in movies, I also tended to lean on the films that were formative in my life. This has a lot to do with simple exposure. I've seen over 2300 movies, yet I there are still a lot of movies I have missed.
This partly an explanation for why the list of Sitcoms tends to be very heavy in things from only the last 20 years.
But there is another reason: character development.
Steven Johnson's fascinating book Everything Bad is Good for You does a very detailed analysis of how television has changed with the invention of the VCR and DVR.
When television took off in the '50's through '70's, there was no way record a show if you were not going to be home. Especially early on, if you missed an episode of Dick Van Dyke, you had no way of knowing if you would ever see it again. Eventually they developed the idea of re-runs and syndication, but even then you had to be home and uninterrupted to be sure you didn't miss anything.
Because of this, early shows made their characters, for the most part, static. If you watch a lot of television over these years, the characters don't change. Ralph Kramden is the same in the first episode as he was at the end. Fred Mertz is a miser from start to finish. Joe Friday is Joe Friday.
The characters couldn't change, because long serialized stories were difficult to pull off. Miss one episode and your investment in the storyline evaporates.
But as we have become able to record and re-watch shows at greater convenience, the stories have not only gotten more complex, but they trust in your ability to see their characters change. If you missed the a few episodes of The Walking Dead, you can catch on reruns, get the DVD, or wait now for Netflix. In fact, Netflix and other streaming services have done even more in this regard because they expect you to binge watch their shows so that you can see the character arcs play out dramatically.
As a result, the more modern sitcoms tend to allow for more character development on their shows. This adds layers of depth, humor, and humanity. I naturally gravitate towards stories that feel like they have significance, By this I mean that the characters go through a journey and are changed by the end for good or for ill. I think other people are also drawn to this quality.
Now it is important to note that this development is not a necessary nor sufficient component of great television. The greatness of some shows is not married to the serialization of story or development of character (e.g. Law and Order, I Love Lucy). In fact, shows that don't have this quality and yet still perform with excellence only service to demonstrate their brilliance. Like an actor who has to perform with his face covered, a story teller who cannot show character development has lost one of his most potent tools at his disposal. To be at that deficit and still create good stories shows a level a greatness through the degree of difficulty.
As we get further down the line to the end, you will find a mixture of old and new, but it does tend to skew towards shows that takes us on a significant journey through changed human lives.