There are a variety of reasons to motivate people through the media, including through stories. Advertisers want to influence you to buy something - you see products used or displayed in movies and this is paid advertising. Whether you really want or need it is not necessarily a primary consideration.
Advertising can be manipulative.
By manipulative, I mean that people are influenced by others - influenced to do something that if they gave greater consideration they might not. Advertising is usually harmless - I sometimes write advertising literature myself, but I relate the ad to real needs and try to influence people to at least have a look at the product. Influencing people to be well-behaved is another reason to try to motivate people. That type of motivation is often coercive and manipulative, even if it includes appeals to sound reasoning and good examples. This often is programming - putting in so much of certain information that the person can see no rational choice but to do what is required of him.