Hmm, did somebody say "jello salad"? Not discouraging anyone else from weighing in -- especially on the decline in popularity -- but you might be interested in a few earlier responses on this subject
/u/Cenodoxus in There are a number of articles on the internet where people make disgusting recipes from the 1950s (ex. ham and bananas hollandaise). Did people in the 50s really eat these?
What was up with the jello obsession the mid-20th century?
/u/davratta in 50s food culture and gelatin and Why were marshmallows popular in the cuisine of 1950s America?