Because the next logical question (as you already stated) simply becomes Okay, where did this God come from? What made it? How does it have these powers? And even if one subscribed to the "Hey all this must have come from somewhere so there must be a God" line of thinking (I don't) that generalistic notion in no way indicates which of the many gods the religions on this earth subscribe to is the correct one.
Your question is a logical dodge. It's like asking, to whom is the bachelor married? Only an Infinite Being could qualify as God. Anything less is angel or demon worship.
The idea that it all came from somewhere actually supports the idea God exist because even a child knows nothing produces nothing. It makes no difference how many degrees a person has they know deep inside the child is correct.
"Only Christ is the fullness of God's revelation." Everyday Hunter
