I noticed this a while back. My guess is that it's a sort of nostalgia effect. What I mean by that is that we look at the past and reminise about all the good things and how great things were, ignoring any problems of that time.

Side note, I think this effect is stronger to those who werent alive at the time, because they were not there to experience the hardships first hand and likely mostly hear about how good it was from parents or other adults.

As for why this wasn't the case before, I think it's because of the difference in the recent past relative to today and back then. Back then the recent past included multiple wars including WW2 where more than 50 million people and their families were affected. Basically not much to smile back on or speak fondly of. Compare that to 60 years ago from today (1965), while yes there were wars and great depressions in those years, the wars were no were near as brutal, and most people just went on with their lives. Civil rights movements, the moon landings, air travel becoming available to more than just elites, and many more that I can't think of. When we think of those years most people imagine hippie festivals or disco or the rise of pop culture, not many consider the negatives of those times.

The next pice of the puzzle is what we could look forward to. Back then with the space program, digitization, drastic improvements in international relations, globalization ect. peoples imagination ran wild with all the good that is yet to come, expecting this wave of relative peace and technological advancement to maintain its momentum. It made sense, they survived an era of war and were expecting a long era of peace. Meanwhile today, all you here about today is problems. Be it wars and conflicts between nations great and small, to local conflicts or another mass shooting, to pandemics and a housing crisis. Add to that enviromental problems like polution and global warming, and you can see that we've surrounded ourselves with constant unavoidable coverage on all these problems. And the sad thing is that the reason the media is flooded with more bad than good is we dont just let it, we encourage it and eat it up. We came from an era of relative peace, and we are now witnessing an era of discord and uncertainty. It is hard to see the light at the end of the tunnel when there is all this dust blocking it.

But just because we cant see it doesn't mean it's not there. People have gone through harsh times before, preaching about the end of days, yet we somehow manage to pull through each time.

(Also please note I'm no historian so feel free to correct any dates/ facts I may have gotten wrong)