I understand not every decade was a clean break, but each decade has fairly distinct defining properties. It feels like most of the 21st century has been a single run on with smaller changes. I know sometimes the definitions don’t come into focus until later, but I’ve been around since the 80s and I can distinctly remember the changes between the 80s, 90s and 00s as they were happening.
I agree with some of your points. I also lived through the 80’s and 90’s and can pick them out more acutely.
But they’re also long ago enough for the survivorship bias to kick in. There are highly specific aesthetics of the 80’s that are regurgitated back to us through media that says “THIS IS THE 80’S”. Think Stranger Things, where they just condensed an entire decade into head nods. Whether or not we personally experienced some of these things, we collectively accept them as “the 80’s”.
Meanwhile, no one is putting Bow Biters forward as iconic of the era, despite the fact that I remember seeing them everywhere when I was a kid. They are not a culturally recognized touch point the way that acid washed jeans and curly mullets are.
I think the average person has a very strong link to the aesthetics of their childhood, too. Someone born in 1995 is going to have a much sharper sense of what the “2000’s” looked and felt like than you or I.