That one begins way back. Originally it was to deny extreme religion in the pursuite of knowledge outside the church in secret because back then people were worse than bible thumpers, but more like a cult back then. First it was that, then after when the age of Charles Darwin "discovered evolution", then it gave scientist the reasons to believe fully that their is no god and when you die, you just die and that is it.
Of course i don't believe in evolution myself as you can see the qoutes in the upper paragraph, but i also do not believe that their is some old man in the sky either nor do i believe in Jesus as my Lord and Savior, niether am i athiest. In short, my beliefs are the earth and all life devinely as a conduite collective consciousness is God which makes science apart of god as well, but genetics on the other hand are sound and logical, and reincarnation is eternal which kind of scares me a little if i overthink it like one paying too much attention to breathing/heartbeat.