That has nothing to do with Buddhism, it's because developing countries dont have govt provided social security so old people have to depend on their kids for support.
But suffering tends to be sharper in poorer countries and some people find it stressful to be around so much less hidden suffering than a richer country where the poorer people are invisible.
> “The church should care for any widow who has no one else to care for her. But if she has children or grandchildren, their first responsibility is to show godliness at home and repay their parents by taking care of them. This is something that pleases God very much....But those who won't care for their own relatives, especially those living in the same household, have denied what we believe. Such people are worse than unbelievers” (1 Timothy 5:3-4, 8)