In logic, the burden of proof always lies with the person proposing the idea. Sure I can tell you why I don't believe or can't believe, but then again I don't have to. I do this out of courtesy. One is absolutely correct in questioning a flat-earther in the same way I must question the idea of god because both of them propose an idea that appears imaginative and contrary to evidence. It is their job to now prove the earth is flat and to prove that there is a god (not necessarily together though!). I take the null hypothesis and presume both are wrong until proven otherwise. This stems from Karl Popper's idea of "falsification" and is an integral gear in the machine of weighing proof.
Try this small thought experiment to understand the burden or proof (or at least the way I understand it). Perhaps someone in the workplace kitchen strikes up a conversation about 9/11 and it fast becomes a treatise about the
government’s conspiratorial cover-up of the attacks. This individual posits a remote-controlled airliner crashing into the towers and a controlled demolition. Now, one could offer counter-evidence immediately to point out the flaws in their argument, but actually, the burden of proof lies strictly with them. They offer a counter explanation to a well-established cause. The explanation is so dichotomous that the burden of proof lies solely with them, extraordinary claims require extraordinary evidence. I see the claim that a deity exists illuminated by the same light. The null hypothesis is that a god does not exist, so any suggestion one does must be backed with strong evidence. It is not up to the atheist to list counter-evidence, the atheist’s only job is to counter any arguments for the god, if he can. US
Indeed, calling me an ‘atheist’ is rather a strange thing. If you think about it, we don’t have a name for someone who is an unbeliever of unicorns, Santa, or fairies. They are not designated ‘a-unicorians’, ‘a-hohoians”, or ‘a-flutterers’. So in the same vein it is odd there is a word for those of us who simply say “no” to the question: Does god exist?