Millennials grew up in the 90s, possibly one of the “best” decades in modern history: good economy, closest we’ve gotten to “world peace,” comparative political stability and “quiet” (the biggest scandal in US politics was Monica Lewinsky), and problems existed but generally seemed to be getting better with time not worse. The 90s were an optimistic time, especially considering the snowballing disaster of a 21st century that followed.
Edit: also advancements in science and technology were bright and exciting, without the constant existential dread of “what calamity have we unleashed this time?” The biggest tech/science-advancement ethical debate I remember was about cloning people, which is a genuine sci-fi-esque moral quandary but ended up being generally moot in reality.