Photo is Harvard students, 1953
If you dressed that way in college today, people would assume that you were as gay as Milo. However, kids in fine private schools still dress in ties for class, and those youths in the photo were probably just wearing something similar to what they had always worn to school. People used to dress for church too. I still do. It shows respect for the occasion. Please do not wear cut-off jeans to church. I am sure God doesn't care, but I do. (And you gals, please do not dress too sexy. It is a terrible distraction for us guys.)
It seems to me that part of the post-war cultural change in the US, and in the West generally, contained a degree of psychological regression, a clinging to childhood or adolescence. I do not know why that happened (decadence from prosperity and comfort?), but there was a time when people aged 18 were adults, viewed themselves as adults, comported themselves as adults, dressed like adults and, in short, aspired to be dignified grown-ups. I know this from my parents, but I grew up after that. Adulthood was difficult for them (military service, war, money, etc) but adulthood is always a deadly serious matter for which children are not equipped.
Dress expectations are superficial for sure, but they still mean something. So do all other cultural expectations. I am most comfortable associating with those who share my cultural expectations. Generally, know what to expect. Birds of a feather...
Solway discusses The Infantilizing of the Academy. I will not blame anybody or anything for the cultural regressions, but it is an interesting question.