With the large population of these two countries, the economic chain will continue to run because everyone definitely needs the food they buy every day, so that food and clothing makers will continue to run more stably. Because each of them also has to work in order to earn money for their own needs, so the large number of people living in these two countries will certainly make the country's economic turnover continue to increase quite well. And it will also be easier for anyone to take advantage of jobs that can make more money.
Population has always been the strenght of economies except the people in power do not know how to utilise it. Even in battles, number speaks louder than strategy.
The economic strength of any nation or people is solely intertwined with their population, both in business and other areas of life. They can achieve more and produce more when they are more. Imagine producing a product to be bought by 1.4 billion people, even if the product is sold for $1 per unit, it simply means the economy just attracted $1.4bn on just one product, and that is a plus for the economy of that nation.