GDP being a measurement for an economy's growth and with the stock market being driven (mostly) by company profits you would expect a tight correlation between GDP growth and stock market performance. After all, a growing economy should lead to a corresponding increase in profit right?
But the stock market is heavily influenced by investor mentality; irrational exuberant buying and panic selling make the stock market far more volatile than GDP ever can be. Just look at the 2001 bubble and 2008 panic sell-off for famous examples. I feel emerging markets are particularly prone to overly optimistic buying to "get in" on the GDP growth followed by overly pessimistic selling when politics get unfavorable.
Also keep in mind that GDP measurements are all done after the fact, the growth that is reported has already happened. The stock market might have already expected the reported growth and priced it in.
A final point: governments and companies in emerging markets have a reputation (sometimes deserved) of poor governance, think corruption, nepotism etc. So even if the economy grows substantially investors might not believe they can profit from the growth.
P.S. What do you base the "no great increase" on? Emerging markets have had a rough decade but that index would have still returned 9% annually if you held it since 2001.