There are countless billions of possible magical beings which could be thrown at the creation of the Universe, yet you don't challenge me on any of them. You don't ask me why Zeus doesn't exist, or Fairies or Elves or any of the other countless possibilities. You dismiss them all out of hand, automatically. You don't lose any sleep at night worrying about the possibility that Allah or Krishna might be the true Creator. Why? What's so special about your particular God that sets it apart from all the other possibilities?
Is there some evidence which shows that your concept of God is the right magical being out of the other billion? Please show me.
Is it more logical that your concept of God is the right one out of the billions? Please explain how.
Of all the possibilities that you could have chosen, does your God happen to be the one you were exposed to as a child? What is the probability that the one "right" one out of all the possibilities available, is the one you happened to be exposed to?
So when you ask me, "Why is it so obvious that God doesn't exist?", I say you already know that answer, and you've used that answer to eliminate all the other possibilities as though they were trivial, barely worth your consideration. You already know there's no God. Everybody should realize it. It's obvious.
While it is true that any one conception of God is unlikely to be true at the expense of all others, that is not evidence that there is no God. It just establishes that mankind's conceptions of God are unlikely to be the truth. God can still exist even if no religion accurately captures the truth of what God is.
I can think of a plausible scenario where differing religions are all valid. What if the differences between the various religions are just separate cultures reaching out to God in their own culturally unique way, with God accepting all of the worship despite the vast differences between some of the religions?
I don't claim that this is the case. Just that it is one possibility.
The truth is, we don't know that God exists, and what his nature is if he does exist. And we also don't know that God doesn't exist. We just don't know anything at all when it comes to the question of God.
And actually, the existence of God and the existence of a spiritual afterlife are two separate questions as well.
For example, perhaps God exists, but does not care at all about humans, and our minds wink out of existence when we die.
Or perhaps God doesn't exist, but there is still an afterlife waiting for us anyway. Maybe when we pray, the prayers are heard by the spirits of our ancestors.
The possibilities are endless. The scenario where there is no God and no afterlife (standard Atheism) is only one of many equally-plausible scenarios.
So that's my argument for hard Agnosticism. I don't know what the truth is, but neither does anyone else.