True, the customs slowly change, and manners do not prescribe quite the same procedures that they did one or two centuries before. But manners remain, informed by the experience of centuries, and slowly modified within the limits of thoughtfulness and common sense. In the last generation it has been regarded as cool to throw off restraints, to mock at formalities, to wear orange socks at commencement, or to belch during a wedding. Part of the attack has been in the name of personal liberty. The mystery of lawlessness doth already work.
Rules are irksome.
Manners are a bother, sometimes even to those who are familiar with them. The big turning point coincided with the jazz age, when Western culture finally accepted Darwin. No longer bound by blue laws or Victorian ideas of morality, people enjoyed a musical idiom that expressed that. Freedom moved further when the naughty music of the jazz era gave way to the raw vulgarity of the 1960's and since. So much for table manners, dress codes, and virginity.