Thanks, Robert.The Geek nailed it.
In the 1950's cars were still pretty much hand assembled at the factory and they had lots and lots of hands on them. It really never occurred to the execs. that having 40 pieces of hardware on a dash board reduced down to 17 was good idea yet. That having just as much bright work and trim on the interior as later cars had on the exterior was pricey. That plastic chrome was easy to make and stainless steel was the opposite.
10 years of evolution and the influence of the American Auto Workers Union had a massive effect on how cars would be built. If they attempted to build a 55 Chevrolet Convertible in 1965 it would have cost $40,000 on the lot and that would be 1965 dollars.
As far as the 1950s versus 1960s cars go, we have to keep things in historical perspective.
Consider the decades of the 20th century.
Between 1900 and 1920, the paradigm shifts in technology were staggering. Of course, the focus of things shifted when World War I broke out. It went on for quite awhile before the US got pulled into it. Finally, in November of 1918, that was over - only to be followed by the flu epidemic that went on until 1920. Much of the 1910s decade was pretty grim.
The 1920s have been repeatedly referred to as "The Roaring '20s". There's a lot to that. With the war and pandemic behind, technology continuing to change daily life, new philosophies on life, lifestyle, clothing, music, etc. - it was generally a prosperous and wide-open decade. And, the latter half of the decade, the stock market took off, making at least some people very rich very quickly.
Then came the stock market crash, bank failures, and the Depression. Everything went to crap in the early 1930s. Then came World War II. Things went further to crap. I mean - really to crap, as the question was whether the rising totalitarian governments would conquer the world. Fortunately, they were ultimately defeated, but at a very great cost.
Finally, things started to clear after 1945. There was still a bit of a rough transition, but things slowly started on the upswing again. And it's no more apparent than the taste in cars.
Let's face it - the industry-wide new car designs which appeared in 1949 were boring. Or, as the British saying goes - "dull as ditch water". Yawn. But, between 1955 and 1960, "living large" styling reflected the times. Tail fins, two and three-tone paint schemes in every imaginable color, chrome and stainless everywhere - there was a "let's enjoy life again" thinking going on everywhere in life (the Cold War aside), including the cars they bought. The Dull-Mobiles of the early 1950s were so "yesterday's news" - longer, lower, wider, more powerful, and shinier was the order of the day. Glitz sells, baby....
By the early 1960s, it was apparent, "umm...we think we overdid it on car styling just a bit", and things toned down. The mega-flop of the Edsel was probably the beginning of the end. True cost control became a little more fashionable. I also think they finally ran out of "over the top" styling ideas which were practical to produce. And, I guess people weren't really that interested in driving to work and the grocery store in cars that resembled rocket ships.