There's not much reason (and even less empirical evidence[1]) to believe that U.S. stocks should follow U.S. economic growth rates.
[1]: http://www.economist.com/blogs/buttonwood/2014/02/growth-and...
[1]: http://www.economist.com/blogs/buttonwood/2014/02/growth-and...
If the growth did continue, then they would make money, but often it doesn't, so they overpaid, so they get below-average (and often below-break-even) returns.
Also, per-capita GDP growth is irrelevant; what correlates positively with equity returns is total GDP growth, including the change in population.
So, on the contrary, this article provides a great deal of reason and even empirical evidence to believe that returns on US stocks should follow US economic growth rates.