Obviously, fashion trends come and change in cycles. We can hardly invent something new in clothing without making it bizarre but we can easily reinterpret old trends in the present-day context. Old fashion can be easily revived by fresh associations, its link with contemporary art, or even social movements. Designers are artists taking their inspiration from trends that already exist as they found well-known basics productive again.
As a rule, trends revive every 15-20 years. What was old is new again, though with certain modifications. An old fashion can easily become fresh and bright with actual patterns and fabrics. The invention of new textiles makes classics, literally, very flexible. Remember old suits without elastane threads? Now compare them to the chic new ones made of high-quality cloth blend that fits just perfectly and is rather comfortable to wear. The difference is minuscule but it helps to make old clothes fashionable again.
So why exactly 20 years are necessary to relaunch the fashion? It happens mostly because of the generation gap. Old trends are definitely new to the younger generation who never faced the invasion of those clothes in the streets. And while their parents want to forget the times when they could hardly find the alternative, the youth takes on creation a new-old fashion. They take inspiration from the past that is nothing bad as long as it acquires a new interpretation.