That chart shows per capita income without adjusting for inflation. It's not very useful for drawing conclusions about real income. And per capita is a simple

That chart shows per capita income without adjusting for inflation. It's not very useful for drawing conclusions about real income. And per capita is a simple average, while looking at medians or quintiles gives you a clearer picture. Per capita, a roomful of middle class workers all become billionaires if Bill Gates walks in.