Something Happened in 2009  

European equities used to be good — more or less as good as US stocks. 

But something(s) changed in 2009. 

One issue was that Europe had to deal with the hangover from the credit boom, with rolling sovereign debt crises and structurally lower growth as it digested malinvestment and deleveraging. 

The USA on the other hand saw years of easy policy + struck "tech stock oil"