I'm surprised to see this counterfactual argument here and wonder if you're acquainted with the history of the word:

Members of this demographic cohort are known as millennials because the oldest became adults around the turn of the millennium. Authors William Strauss and Neil Howe, known for creating the Strauss–Howe generational theory, are widely credited with naming the millennials. They coined the term in 1987, around the time children born in 1982 were entering kindergarten, and the media were first identifying their prospective link to the impending new millennium as the high school graduating class of 2000.

I remember this very well because I was a member of the class of 2000. 🧓 and yes, I do remember the 80s.