The simplest reason could be that for any amount of money invested, these countries typically growing economies like India and China have a high rate of equity dilution resulting in a decrease in the EPS (and hence a reduction in growth seen per share brought).

This item was originally discussed here.

This is also clearly seen from the plot below by an analyst at Morgan Stanley:
(click on fig to enlarge)

Country-wise comparison of the average earnings growth with the annual dilution  - highest for high growth countries.