God did not turn His back on them but they have turned their backs on God. According to the Bible God is not willing that any should perish but that all will come to repentance. I met some atheists in my life and i even tried to share the gospel with them, but they refused to hear the message. They would rather talk about other things than hear about God and His plans.
On the outside they look like everybody else and even appear worry free.
By the way I wrote God can not save them. Why ? The Bible says without faith it is impossible to please God. And ignoring God is obvious lack of faith.Yet atheists mind their own business and even trusts what they have.
Russia I understand were taught that there is no God but when the iron curtain fell and the gospel was presented to them, they repented of their unbelief and became Christians. Maybe not all but some got converted. Those who surrendered to Christ will be saved but others who continued with their way of life and thinking will miss salvation unless they change later on.
The gospel I believe is being presented to the whole world, except in places where they are not allowed.
Again God loves atheists too but atheists need to love God back.And if they do they will become theists. Can you imagine that ? all they have to do is remove "a" to be believers in God. It may not be as simple as that but it is a start.