This isn't enough of an explanation. South Korea is denser than India, but only by ~20%, and India's fertility rate is more than double South Korea's. Taiwan is

This isn't enough of an explanation. South Korea is denser than India, but only by ~20%, and India's fertility rate is more than double South Korea's. Taiwan is denser than South Korea, but its fertility rate is more than 50% higher. South Korea really is an outlier. You might also compare the United States to its peers in Europe--fertility isn't that much higher in the US (and is lower compared to a few European countries that are much denser).