Novelist and social critic Allison Lurie wrote a fascinating book back in the 1980s called The Language of Clothes. It includes a discussion of the dressing habits of the elderly, and she noticed several trends.
One was towards a greaternformality in dress, with an emphasis on looseness and comfort. One sees a fair number of older people walking around in sweats who obviously do not work out.
Another tendency she noted was the one you describe. As previous posters have written, it is a matter of long-time experience.
There was a general easing of the formaility with which people in America dressed during the Twentieth Century, and great reduction in the degree to which one could distinguish a person’s social class by their dress. In his memoirs, Nikita Krushev expressed surprise that he could not actually tell that Nelson Rockefeller was a mult-millionaire from the kind of suit he wore. Somewhere in the back of his mind, I expect, he was picturing a three piece English drape suit with a huge gold watch chain.
These changes came in spurts.
Up until the late 1940s it was very common for the upper and upper middle classes to dress formally for dinner at home. Writer Calvin Trillin has told a funny story about this; when he attended Yale in the 50s his roommate observed that his family had not “dressed for dinner” since the war. Trillin, who came from more of a working class background, was shocked, and said his father would never stand for that. He thought his roommate meant he could just turn up at the table in his undershirt.
Coolidge’s son John recalled that his father had a fit once while they were living in the White House because he came to family dinner without a tie.
Coolidge’s time in the White House–the 20s–was a time when the dressing habits of Americans loosened up some. It is said that Coolidge was also was upset that his wife Grace, a fashion trend-setter–was seen in public wearing breaches when she went horseback riding.
The 60s were an even more notable time in terms of loosening dress restrictions. In the 1950s middle class women wore white gloves when they dropped over to a friend’s house. We laugh now at the way the parents dressed on Leave It to Beaver, but that is a fairly accurate depiction of how people in their social strata actually dressed. While it was relatively unusual for a woman to wear pearls as often as Barbara Billingsly did, she has explained that this was her habit at the time in real life; she thought her neck was unattractive.
I dimly remember that when I was a preschooler in the late 1950s and early 1960s my father would take me for walks on the weekend. He would dress for the occasion, putting on a suit and tie. He would also wear a fedora. It was customary in my family–a fairly normal middle class suburban one–for the boys and men to wear suits and ties whenever we went to church or to a movie until about 1970.