Moving a discussion that got started in the obits thread here:
Agree with mb's long post above. At least until recently, what we think of as "decades" actually tend to run 2-5 years behind.
The pictures we have of the "50s" with the poodle skirts and the teenagers dancing to Elvis or Carl Perkins rock and roll music at the sock hop, really didn't start until 54/55. The early 50s were more like the 40s. And our idea of the "50s" really ran into the mid 60s.
And what we think of as the "groovy 60s" was really more like mid 60s into the early 70s. And so on. So what we think of as the 80s persisted in large part into the early 90s.
Beyond that, those trends are really defined more by the "kid cultures" of the era. Adults tend to hit their 20s and then sort of... stay the same. They tend to stick with certain music and are less open to newer music, they tend to not follow new fashion trends as closely, and when they do adopt new cultural themes, they adopt much slower. On the other hand, kids tend to be the vanguard of the ever-changing culture.
With that as a basis, Seinfeld was a thoroughly adult show. It really never had any kids nor any kid-related themes. Its characters were all adults into their 30s, mostly in professional(ish) careers, doing adult-y things in adult-y ways. So as an adult show, grounded culturally in the 80s, it never really picked up the culture of the 90s. It was conceived in the 80s and started as an 80s show, and remained that way throughout its run.
That's just my hypothesis and my opinion of course.
Vis-a-vis decades:
I think that what we think of as the Roaring 20's was actually less than a decade. IIRC, there was a bit of an economic downturn at the end of WWI so the "Roaring" didn't really get started until later in the 20's. Then it ended suddenly in late 1929 with the Stock Market Crash.
The 30's are The Great Depression and that was basically from the stock market crash in 1929 until Military Orders from Britain and France lifted us out of the recession of 1938ish.
The 40's are WWII but I would include the immediate post-war era and even the Korean War (1951-1953). That makes this a ~15 year "decade" from roughly the Munich Conference to the Korea Armistice.
What we think of as the 50's, IMHO is basically from the end of Korea to the beginning of Vietnam so roughly 1953-1965.
Defining the "beginning" of Vietnam isn't nearly as easy as it sounds. The French were fighting Communists in what was then called French Indo-China even before WWII. After WWII we were "involved" with the French* but our involvement was very limited. Once the French pulled out, South Vietnam basically became an American dependent but even still out actual boots on the ground were limited to a few advisors. Large numbers of American Combat Troops didn't start fighting and dying until after LBJ's election in 1964^. I use that as the definition.
What we think of as the 1960's, IMHO is basically the Vietnam era so roughly 1965-1974.
I actually think that what we think of as the 70's was a REALLY short "decade" because even by 1979 most of the music has a very "80's" feel to it.
With that as a basis, Seinfeld was a thoroughly adult show. It really never had any kids nor any kid-related themes. Its characters were all adults into their 30s, mostly in professional(ish) careers, doing adult-y things in adult-y ways. So as an adult show, grounded culturally in the 80s, it never really picked up the culture of the 90s. It was conceived in the 80s and started as an 80s show, and remained that way throughout its run.
This is something I hadn't really considered before but it is an interesting point. If Seinfeld had been about HS or college students it would have been influenced by AOL and the WWW because those things were becoming prevalent in the 1990's while the show was still on but since it was about, as you put it, adults "doing adult-y things in adult-y ways" that never came up.
