I don't know the "real" answer, the one that has research behind it. But, it seems to me we are socialized this way. We believe that stuff makes us happy. Advertisers lead us to believe we will be happy if we drink this beer, buy this car, wear these shoes, and so forth. Then, our friends, neighbors, and so forth reinforce it.
Soon, whenever we can't get what we want or need (love, fulfillment, peace, etc.), we fill the void with things. For a short time it makes us happy. When that fades, we have to buy something else.
The rich, celebrities and so forth are held up as role models, it's easier to understand, more visible than looking at say, a Buddhist Monk, and saying, oh, he has the key to happiness, lets follow him. As is often true, I guess we want the easy answers.
Going to the store for a new purse is much easier than searching our souls, working on our relationships, and so forth.