Yes, what we call "fashion trends" pop up and off they go !
I don't know what really governed or influenced them, say 20 years ago, but today perhaps there's a growing influence from interaction on the Internet. It's certainly something which consumer market-watchers are keeping an eye on, as the increasing useage of the Internet must fuel ideas and interactive influences.
20 years ago, was it the traditional media which drove trends ? Who knows, but today, the greater the mass communication of media such as the Internet, the faster the turnover in trends and fashions, imv.