I think it's mostly as simple as money having marginal utility. The first $30k a person make per year goes to absolute essential (ie. food, housing). The next $

I think it's mostly as simple as money having marginal utility. The first $30k a person make per year goes to absolute essential (ie. food, housing). The next $30k goes to really nice the have things like better transportation, medicine, etc. As a person makes more money, each additional dollar has less of an impact on their life.