An alternate hypothesis is that starting in 1971, labor union participation in the US began its decline. Rather than needing to use leverage, as you suggest, t

An alternate hypothesis is that starting in 1971, labor union participation in the US began its decline. Rather than needing to use leverage, as you suggest, they just directly filtered the increased productivity gains to the top of the company. Also, I'm not really sure that your graph shows anything except that the financial industry has been growing since the 40s.