So, why do you think is India the world's second largest economy, then?
they made good economic reforms at the right time i guess. Instead of potentially remaining an insular economy, they moved towards becoming a proper free market economy whilst retaining the appropriate protections in certain areas. Also starting to get good international relations with the U.S. U.K, France, Germany, Australia, Japan and other asian nations certainly helped their textiles industry greatly at the time. This probably saw them overtake China as the world's major manufacturer of clothes and by the 80's, they became the choice for manufacturing products in general.
Now, I guess having major commercial centers (think about it, Karachi, Lahore, Delhi, Mumbai, Calcutta and Dhaka all have populations of over 10 million and are all in their own right, major centers of trade and commerce) would help, especially when you compare it to a similar sized country in China (where cities have developed, but the big cities are really Shanghai, Beijing and some of the cities in that Pearl River Delta region). I suspect though that is a by-product of the countries success though, still, having that many centers of trade has made India a lot more attractive to investors over the years as they have options in where to invest. The fact that it was open to that investment (i mean their were restrictions but at least it wasn't closed of like China) did a lot.