Think about all the change that took place between the years '75 and '90. Think about the drastic difference in the styles, cars, music, movies, language, etc. All the evolution that took place through the 80's. All that hair spray and acid-wash that went relevant-to-archaic in a single breath. The pitch and roll of trends through this 15 year window was drastic.
Anyway...
Now think about the years '00 through '15. The same amount of time, yet there seems to be a much smaller overall evolution in the areas of style, cars, movies, music, etc. There certainly has been change, but is seems much, much less drastic then the aforementioned decade-and-a-half. Would you be able to see a woman walking down the street in a '00 hair style and really notice? Probably not. Do you think you could notice a hair style from '75 if you saw it in '90? Probably so. If it was '90 you went to a '75 themed party would it look all wacky and different, all filled with feathered hair and rainbow suspenders? If it was '15 and you went to a '00 themed party people would probably just be wearing Destiny Child, or maybe Matchbox 20 shirts.
If this is true (I think it is) then it begs the question "why?" I've thought this through, and in my uneducated opinion, I'd guess that it has something to do with the internet's increased ubiquity in our society, and the east with which we have access to it. My hunch is that people only have the ability to process (or maybe "care about" might be better) only so much change. With the way internet memes come and go (or any other various concepts pertaining to or perpetuated by the internet), maybe our collective attention is drawn away from the angle of our tail lights or the style of our hair, even if ever so slightly, and more-so drawn into tablets and smart phones and we simply pay less attention to any exterior change.
Anyway...