The explanation needs to be simpler. When a store has a sale, they do not do that to lose money. The profit is less on each item sold, but they make more money by selling more items. Rich people are in a different situation and can adjust their earnings, whereas most of us can't. Sometimes they even avoid earning because of taxes. Lowering taxes is like having a sale on high incomes. Lower tax on each dollar, but more dollars to tax. Additionally, high incomes involve hiring someone to participate in making the money. More commerce means more shared wealth. The benefits go around and around.