Supermarkets are specifically designed to take advantage of human psychology. Over a hundred or so years, these stores have learned what people will do when they aren't paying all that much attention, and have harnessed those tendencies to get you to purchase more items, and specifically items with the highest markup for the highest profit. The science of marketing is so successful that you can go into a supermarket in a new town with a name you've never heard before and the layout will be the same as any other store of its kind.
What does this have to do with video games? That's explained, also, as the same type of inducements are there when you browse through a Free to Play site and encounter multiple opportunities for microtransactions that are specifically placed and timed to entice you to go for it. The cost may be small, but it adds up if they lure you into doing it over and over. This video is only 7:30; the rest is an ad.