There is no such thing as a successful atheist country.
Like it or not, humanity appears to require religion to thrive.
Faith begets faith in humanity and on a smaller scale, community. The community must be homogenous for members to find contribution fulfilling instead of depriving (surrendering resources to a geographically present, invading outgroup). “Diverse” communities corrupt and become parasitic whatever the excessive funding or weak leadership (see: The Third World for the results of decades of patience and tolerance). Anyone with computer access can research this.
Thankfully, atheists reproduce less because their superior intellects have trouble reading fertility replacement charts.