The short and obvious answer to all these questions is that they do it because it increases their sales and profits. The more interesting question is why these marketing tricks are so successful in persuading us to part with our money. But that's easier said than done.
Value is a subjective concept - it's in the mind of the beholder.
To judge the value of something, we need a frame of reference - a point of comparison. What this means is that businesspeople can influence our assessment of the value of a product by manipulating the context in which we judge it, especially the other products with which we compare it. The mark of a successful shopkeeper or salesperson is their intuitive understanding of the quirks of human nature. 1995 issue of the California Management Review . You may imagine they do this on the simple principle that offering a wider choice increases their chance of making a sale.