Because we are human. What it entails to be human is greed, selfishness, self centeredness, and our lovely frontal lobe which is responsible for all the things that I just mentioned. I think the worse curse on humanity is greed. No other animal has it. Only the human. The main reason is to of course advance in life. But at the end, does it really matter how much you advance if you’re already successful and making a 6 figure income?