For me it was a habit. It was what I'd been brought up to believe. I didn't really question it until (I'm slightly embarrased to admit) my late 30s.
I'm now a confirmed and happy atheist.
I was brought up in a family which went to church, and made me go even though I didn't want to.
Even at age six I questioned it, but was made to go to Sunday school (bad enough) then 'youth group' (absolutely mind numbing).
Evenually, I was leaving the house at the right time, coming back at the right time, but not going. I would spend the time reading the paperbacks in the newsagents. Mum caught on, and gave up on trying to make me go!
So why did she believe, but I didn't? I have no idea.
On the issues of creation, evolution, what was there before... I have no idea, but actually I don't feel any need to know. Whatever it was, it was.