I think it has a lot to do with cultural taboos and media whitewashing. In the 80's there was lots of media from the 50's on TV, like Donna Reed, Leave it to Beaver, The Andy Griffith show, etc. The popular media of the time is mostly about rich white people dealing with simple family problems that result in teaching situations. In the 80's we had Married with Children and Hard Copy, which I can't imagine being accepted on television in the 50s. In the 80s, the 50s seemed so different, a gentler and easier time, without the same strife (which is untrue, mind you). The 80's are relatable because we recognize the same problems in them that we see in ourselves today.
In short, it's not that the society of previous time period was more different during these ranges, it's that our perception of that previous period through their surviving media was more or less relatable to our current experiences.
In short, it's not that the society of previous time period was more different during these ranges, it's that our perception of that previous period through their surviving media was more or less relatable to our current experiences.