Sometimes asking people will give you true insight, and sometimes it will give you false insight because the people themselves don't consciously know and make things up that seem right but are not; or, a behavior or decision is the product of a chain of other things that's too complex to reason about or communicate easily even if each link in the chain is consciously known.

On South Korea, you might want to consider this chart instead: https://www.macrotrends.net/global-metrics/countries/KOR/sou...

KOR's Fertility rate has been under 1.25 for two decades. It follows then that "stable" population can only be the result of three factors:

1. Pushing the population curve out through longer lives;

2. Immigration;

3. Time-effect offsets of the fertility rate; for instance, if it's the projected fertility rate of females born in a given year, it would take roughly 20-40 years for the fertility rate to have its effect on the population curve.