In a free-market economy there is constant movement. Quintile distributions themselves mean very little. But in a market economy, income is created by voluntary exchange between people. Each individual owns the income he creates. It is desirable for those who serve others well to have higher incomes than those who don't, because those differences provide incentives for people to try to serve others as best they can.
Widespread prosperity comes from widespread efforts to serve others well.
If you choose your occupation on the basis of what you like to do without regard to what other people are willing to pay you to do, you may end up happy but poor. I like to sing. But no one is willing to pay me to sing. So I talk and write for a living. If I chose to sing for a living I would be justly poor.