Consumerism teaches the population that fads where you buy and display things is a form of socialization. With limited time, you can actually build a passable personality out of consumption habits and the constellation of activities around them. I know people that more or less do this.

Companies are all trying to be the next and longest-lasting fad because it means high profits. A fad is just sudden large demand, which translates into a large volume of profit if they can make enough supply. For Barbie stuff? Just make more pink items and maybe brand some of them. Easy way to ride the fad and these folks wrapped up in the spectacle will do most of the work to sustain it.