I’m not Catholic btw but this is the reason as i see it. It all started with the 1400-1500’s when the Pope held a long standing view that Christians could not charge Christians interest on money loaned. This was not good for business so when Luther and other protestant fathers challenged the authority of the Pope, the wealthy boyers (wealthy land owners) saw this as a opportunity to discontinue the no interest laws. So in promoting the reformation and kicking Rome out, they improved their bottom-line.
On to western europe and the USA. The reformation/protestantism naturally leads to athiesm:
-turn back on church authority as the holder of true/right interp of the Bible->make interp of the bible up to the individual which means there is no true authority on interp->their are so many sects claiming to be the right interp all interp is relative to the observer->there are many books of faith out thier Koran, book of Mormon, Bible etc. so all religion is relative there is no right religion-> everyone is right therefore no one is right->why believe in God at all?
In my view the string of athiesm as a major player started with the reformation/protestant movement which was started for economic reasons.