Why get rich?

You might have seen this chart, which shows different professions' household income during childhood vs their income now:

A lot of people have focused on the fact that artists' incomes 'fall' more than any other group. It reminded me of this quote from the American Founding Father John Adams:

I must study politics and war that my sons may have liberty to study mathematics and philosophy. My sons ought to study mathematics and philosophy, geography, natural history, naval architecture, navigation, commerce, and agriculture, in order to give their children a right to study painting, poetry, music, architecture, statuary, tapestry, and porcelain.