In earlier times there was no reason to believe in anything else. I guess it was a choice between different religions at best. Any preference was probably political rather than religious (as is human nature)
Besides religion has the razzmatazz... The Miracles, Magic and Mystery. Which the atheists sadly don't have!
Which is another point that I believe, people come to their religions/beliefs (or lack of) through attrition, quite often (more often I think) people adopt the religion of their parents and what we're seeing in the west now is people making choices.
