One of the "reasons" (and I use that word carefully as it generally has nothing at all to do with Reason) why many people, who perhaps do not believe or care whether the Adam and Eve stories are historical or not, hold on to the idea that there must be a god behind creation is twofold. One is stated most clearly by the alarm the catholic church recently stated in an article in Telegraph.co.uk "Cardinal George says... he, and the whole of the American Church, must be praying that the certainty of unbelief wears off as the “new atheists” have children and face the prospect
of mortality." In other words, their hope is that people will get scared(by him) of going to hell and will give up the "new atheism".
The other reason is a bit more nebulous and difficult to understand. It is simply a belief that somehow ancient people knew more about god than we do and were more in touch with spiritual matters. There are plenty of monetary reasons why new age and eastern religions perpetuate this idea...I mean, after all, would you really buy a bunch of crystals for gas if you hadn't been told by one of these ancient "wise" spiritual leaders how helpful they were? But the question one has to ask oneself is just WHY we believe that a bunch of spiritual leaders today, who got their "information" from ANCIENT witch doctors and fortune tellers who knew next to nothing about the earth or the body or the universe, would somehow know everything there is to know about god? Of course the easy, no brainer answer for those who wish to keep this belief is to say that science and technology get in our way of knowing god. Yet, if these wise spirit guides had a direct line to god, then why didn't god tell them more about how the body, for example, really worked? Even just a smidgeon more??? (If you think at all about what doctors in the past did in the name of science and discovery, it might increase your own questions about god's lack of communication skills on these matters)
And more particularly, in the case of the bible, why didn't god just communicate the real stories of ancient people that he helped along the way? Why make up stories that could never be verified? After all, god being god would know that god was telling fibs and that we would find that out one day.