It could also be a matter of population change. Old Christians are dying. Children are being born into single family households that have rejected God.
From an earthly perspective that’s certainly part of it.
From a biblical perspective, everything is as it has always been. Every single one of God’s elect, all of those chosen in Christ from before the foundation of the earth, will come to Christ and be saved.
“All that the Father giveth me shall come to me; and him that cometh to me I will in no wise cast out.”
—John 6:37
“Blessed be the God and Father of our Lord Jesus Christ, who hath blessed us with all spiritual blessings in heavenly places in Christ: According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will, To the praise of the glory of his grace, wherein he hath made us accepted in the beloved.”
—Ephesians 1:3-6