I can guess there would be some reasons why people buy things if they not essentially need them. Firstly, people just want to be look special, which make them buy an expensive bag or a watch if they already have one. It seems that they believe what they have can show what they are to other people. However some new products are expensive, they don't care much. Secondly, people buy stuff just they are sick and tired of using the same things for a long time. For example, especially in my country, I can easily find many young people like to switch their smartphone at least every 2 years even if theirs work well. Thirdly, some people want to follow the current trend. They might think that if they use the same new product, they are with the new popularity.