Fashion depends on a constant stream of change to get people to buy the latest in-thing. Think about the design dimensions that are possible link here. How many inches above or below the knee can a hemline be? Are they going to copyright that? Take the next step. How many inches can a skirt flair? How many pleats? How wide each pleat? How many colors? How high the waistline? I'd love to be the lawyer defending a copyright infringement case in court. Ask the plaintiff what distinguishes his design. How can he answer?
It gets only slightly better when one considers the example of pretty obvious knockoffs. But big-name fashion houses aren't going to produce them. So now we are in the realm low-end fashion. Isn't the copied better off accepting the emulation as what high-end fashion is all about? The design is obviously widely admired. The original must be worth several times what the knockoffs have to sell for. And why worry? The next season will bring a whole new set of fashions. That is the definition of fashion.
Copyrighting fashion is a contradiction in terms. It will kill innovation (and profit) in the industry. Like so much else with intellectual property protection..