[DJN]

It’s because where the money goes is where it circulates, which ultimately affects the GDP.

Every dollar that leaves India, Nigeria or any other developing country is one less dollar that can pay for jobs (plumbers, electricians, doctors etc) in the local market.

South Africa used to have very restrictive currency export controls partly due to apartheid-era sanctions, and one consequence is that it stimulated domestic production and innovation, perhaps far more than any other African country. They’ve now relaxed those controls but it is arguable that they were necessary at that stage of their economic development.