Denim has been around forever! It has served people as work wear, casual wear and high fashion. It always survived changes in fashion trends, sometimes with redesigns to keep up with consumer appetites, but even the long lived original designs are still in production.
Apparently, jean manufacturers are experiencing a significant decline in sales (along with the stores that sell their products). Domestic sales dropped 6 percent last year with a significant decrease in sales to women a contributing factor. The competition for consumers dollars and consumers limited budgets, has become very intense. The economic climate has severely impacted consumer's buying along with fashion trends showing a change in consumer preferences.
There has been a growing preference for casual wear and leisurewear as consumers are moving towards wearing clothing for comfort. Athletic wear like leggings and yoga pants have increased their market share moving from limited applications to everyday wear. It's hard to know whether this is just a result of short lived trends or an indicator of a major change. A concern of manufacturers is that once customers have left, it is hard to win them back.
http://www.nbcnews.com/business/consumer/denim-real-danger-going-out-fashion-n176211
http://fortune.com/2014/07/18/why-are-jeans-sales-so-bad-blame-sears-and-penney-and-jeggings/