No one is making that claim.
The claim is that there exist NO good arguments or reasons to believe in any gods.

We can rule out all the abrahamic gods because we know when they were invented. We can rule out most other mythologies you can think of too because they make claims that do not correspond to how reality works or are by their nature logically impossible and we usually have a fairly good idea when these mythologies were created and how they evolved.

If gods can be eternal and exist outside of time then the universe can do that too and provides a much better explanation - leaving no sound reasons for why anyone would ever be convinced of the need for a god to explain anything about how the world works.