2.1 is the replacement rate for well-developed countries. It does not apply universally to all countries.
For example, the US had a fertility rate of 7.0(!) in 1800 and saw no significant population growth due to births because most of those kids died well before reaching the age of reproduction.
Historically, fertility rates have always dropped once basic standards of living have managed to get rid of excess child mortality.
Unless those countries have increasingly western lifestyles, stable political systems and growing economies, then it actually doesn't matter. The grim reality is that all those places have substantial modifiers on their death rates, and aren't exporting their increasing population to the world in any meaningful way.
We know from experience that if those places actually started to improve, then the birth rate would drop precipitously.
For example, the US had a fertility rate of 7.0(!) in 1800 and saw no significant population growth due to births because most of those kids died well before reaching the age of reproduction.
Historically, fertility rates have always dropped once basic standards of living have managed to get rid of excess child mortality.