It's getting harder than ever to become a self-made billionaire. But inheritances are still going strong.

• Billionaires minted through inheritance outpaced self-made billionaires last year for the first time in a decade.
• Experts cite deteriorating conditions for building wealth through entrepreneurship.
• The divergence between the growth of inherited wealth and the reduction of organic opportunities for the middle class is likely to keep accelerating, economists say.

Economists say the path to self-made riches in the US is shrinking, and there are more riches being passed down through inheritance these days than are being created through entrepreneurship.