Gaz, it comes from my previous post about Atheism being a mean to fight influence of religion.
Just a matter of expression in this case.
Modern Atheism has developed in two distinct directions.
1st being a tool to fight church. At the start of the 20st century we have a global rise of communism which started in Russia. Church has always had huge political influence in Russian Empire and Czars never went against it. It was, as Gazz noted, an extremely useful tool to control peasants. Fear of unknown, together with past middle age mentality, a perfect combination to make one obedient.
2nd is a modern one. People became self sufficient. It's no longer about making sure you have enough food on the table, its about having the best life you have. Material things are taking over the need to believe in something. Way of life makes us to relay on our own strengths rather then the gold plated cross in church and holly guy in clothes which cost more then you earn in a year. Predominance of science also made sure that we can explain more and more in the world around us.
Those are my basic thoughts on the matter.