People were just less anxious and depressed back then, especially according to recorded stats the most severe was the 68/69 it was basically the peak of huge human gathering, between marches, students protests, Woodstock, Summer of love, Beatlemania, surf culture. In short nobody gave a darn about the flu.
It seems to me, people nowadays are more concerned with existing that living, and somehow have convinced themselves to hold out long enough and they'd be able to reach immortality.
it's like they don't know that sooner or later they'd die anyway and that the secret is to live in the moment and enjoy life , stumbling on their way to the grave with a smile on their face due to the fun they had along the way.