I can't answer as to why philosophers in general are curious about god (to attempt an answer to that is a philosophical discussion itself, I believe), but I can say why I'm interested (just to give you another sample point).
1. Where did I come from?
2. Why am I here?
3. Where am I going?
Re. 1, your fundamental question of origins. How did matter and the universe initially come to exist? You can go back to your Big Bang, but that's still contingent on the initial bunch of matter being there to begin with. The god concept tries to deal with this. You wonder about something outside the whole concept of matter and existence (and outside the concept of "something", for that matter), and you apply the name God.
Re. 2, your basic meaning of life question. I struggle a bit with existential depression. I do this because of that, and I do that because of that, etc. Where does it ultimately lead back to? The idea of a god initiating reality for a reason tries to answer some of that.
Re. 3, the what happens after death thing. I don't want to die, and it's hard to accept the finality of that. To be honest, though, that's more of a "gee, wouldn't it be nice" thing than a philosophical thing to me.
The first two questions are the kind of core things that philosophy is made of. To me, the whole "god" thing ties in with that pretty naturally. Though I think "religion" is usually the flipside of philosophy.
As they say, philosophy is questions that will never be answered, while religion is answers that will never be questioned. Though I think the latter is not true of all practicing "religious" people; I think some of them are willing to question, and are always open to re-evaluation. Unfortunately, that seems to comprise the minority of both theists and atheists.