why ?

Because often a person works harder than others or has a better idea than others, which leads to more money. If everybody were paid well regardless of achievement, there would be less incentive for hard work, invention, innovation, education. That is why the communist governments do not do well and have a very low standard for living for all, except government people. It is in the nature of many people to want more, to be above others, or to achieve more, and any system that ignores this basic fact fails.

Cause a lot of the rich people are greedy and take a lot of money we could have.