Most people idealize the time period upon which they were young, not for the fact that it was good or bad but for their memories within it. A large portion of modern Americans were teenagers during the 90's and are the mom's and dads of today.
When they go back to the 90's, they aren't seeing the cartoons and the music, they're seeing their previous boyfriends, their good friends, their physical peak, and what life they had before that has since left them. They are seeing their favorite memories, when they see the 90's.
If you ask a 1980's teenager whose since grown up what time period was their personal favorite based from experience, the average one will idealize the 1980's in place of the 90's and for the same reason.