Reuse of successful concepts
Companies and their people often take a concept that has proven to work before and apply it to another use. Concepts created online get offline and vice versa. When the film "Harry Potter" became successful, many new episodes appeared, which multiplied its effect. Everyone was so excited, that soon there was demand for Harry Potter books too. Suddenly, Harry Potter was everywhere. There is nothing wrong with taking a concept and applying it repeatedly. The problem is that all good things get overused.
"Avatar" was another highly successful film. Its creators said that their profits were so high partially because of the 3D version in addition to the regular one. Many people wanted to experience the difference, so they took the special glasses. Then, the game Avatar for iPhone appeared, creating a psychological effect, so the people that watched the films felt that they need the game too. Of course, they were ready to pay for their crush.