Nostalgia is a factor
In the modern age we live in, it's easy to get caught up in all the new tech gadgets that seem to come out every single day, which results in a nostalgia feeling when you see something that once peaked your interest that would or could be redeemed as "outdated" in today's times.
With the craze of Star Wars and old western TV shows like The Lone Ranger there is a need to provide content to those audiences that want to relive or provide a way to relive their past. Say you draw a design of Jim Morrison and a fan of his purchases your stock illustration to write a blog article showcasing his life's story, you had a part in making that and filling a need in the market at the same time.
Nostalgia comes in all shapes and forms... it could be seeing a book you read once, or a movie you have seen, and it could even be talking to an old dear friend you have not seen in ages... Nostalgia is what ever triggers a memory of a time in your life... "usually a happier time." Providing a link to that realm the possibility of stock image sales can be endless!
In closing it's important to state that contributing to niche markets like that, their is heavy competition in the nostalgia field, so ever work that you intend to submit to it should really be your best kind of images.
Photo credits: Gluestick.