Albania or Turkey have lower standard of living yet a high fertility rate.
Religion.
But you were just saying it has to do with wealth and standard of living.
A 100 years ago people were ass poor yet had 4-6 kids on average. Here in the federal state of Styria in Austria politicians thought "Hey, let's make the Kindergarten free and finance Afternoon school and supervision like they do in France", yet people still don't get more children.
Money has little do to with it.