I am a young Xer, almost an old millennial, kind of on the cusp. I've wondered if this is a cognitive artifact of my age in the 90s, teens to 20, but I have asked older and even a few younger people and many have also expressed nostalgia for that decade. Boomers and much older Xers often agree.
My teens were rough anyway. It was not my personal best decade, but I would go back in a second... not necessarily literally but definitely to the zeitgeist.
I find myself unable to describe the optimism of that time to people who were not of age during it. The best I can do is encourage people to watch some old Star Trek TNG. You couldn't even write that today. Dark edgy music and culture was in, but that was an artifact of the optimism. Nobody wants a Nine Inch Nails or early Tool now because the world is darker than the music. Pretty Hate Machine would be journalism, not harmless cathartic emotional escape and fantasy.
For my money the optimism ended decisively on 9/11. The shift was incredibly deep and profound. We have never recovered, though a rally was attempted in the late oughts. That rally crashed into resentment driven identity politics; the alt-right and its fellow travelers or "cancel culture" on the other side. Superficial optimism doesn't stick and won't until we get past 9/11 and all it seemed to mean. The terrorists won.