We have an instinctual desire to be consumers. Every reproducing living organism is designed to have endless needs and wants. This design helped us survive in the past as a species, but it may very well be making things worse in the modern era.
This never ending desire to consume, was an instrument that instructed our bodies and brains to transfer our healthy genes to the next generation by being curious, hungry and horny all the time. The need to acquire knowledge in order to live as comfortably as possible is another manifestation of consumerism, which existed in the Caveman era too.
Now, the avenues to consume our basic needs are saturated for people who live in the industrialized world. So a huge vacuum is created in our instinctual will to consume, leading us to find other means to fulfil this biological need. Hence, Capitalism.