It's caused by one thing called Greed
Why do we not feel satisfied in life? It's like we keep on wanting more and more. why is that?
Whenever you do something considered pleasurable, a chemical called dopamine gets released to the brain and then when you next want that sensation again you just try to achieve it again by doing whatever it was that made you release dopamine in the first place... like eating or buying stuff.
Many humans were raised with the desire to acquire material things.
It takes hard work and even greater control to take only what is necessary to survive.
Many people never make it just like that, but instead surrender to greed. I'm sure you've seen many examples.