If you were to ask why a film is created, some film makers may respond with “we do it for fun”. Which may be true to some extent, although I highly doubt their work would continue without a fairly hefty pay packet being included.
Money is the main source of why transmedia story telling is used. The formatting of a single story across multiple media outlets is all but a money spinner, for which relies heavily on the success of a book, in order to be turned into a film. For example, the 7 book series “Harry Potter” was a success on the platform of books, so therefor it was able to be transferred across to the digital platform of film with minimal risk of failure in order for the chance of making money.
Of course, while the major film making companies make money, someone has to lose money, right? The loser here financially, unfortunately is everyday movie lovers like myself. This is because we are the silly suckers which get roped into paying for the movie tickets, in order to send the money to the top dog movie producers and actors.