Paraphrased: "How come Christians never let me argue against THEIR God? Instead they always want to talk about why there's something rather than nothing, or first causes or things like that! I don't want to talk about those gods, I want to talk about theirs!"
Except an atheist isn't supposed to deny only that specific God over there, but God and gods, period. And understanding those fundamental attributes of God is, and has historically been treated as, key for understanding the specifically Christian God. Imagine trying to justify the existence of whales to a man who denies the existence of all aquatic life. You try to explain the plausibility of how a creature could move and live underwater, and he just gets angry: No, he wants to talk about WHALES. All this talk about fins and algae and so on, he doesn't want to hear about it.
Whales are so improbable and ridiculous-sounding after all - why, how would they move and what would they eat?