I'm not an atheist, I'm agnostic. I'm guessing most of the people you classify as atheist are actually agnostics.
The easiest things to determine existence are those that we can directly see and touch and move around; call that "local existence." The next things are the things we can infer from repeatable measurements and/or observations and/or experiments. That covers pretty much everything else - planets, distant galaxies, merging black holes, electromagnetic waves, speed of light, atoms, etc etc.
So, when you ask me does such a thing as X exist? I answer with another question: does X make a measurable difference anywhere anyhow? And does that alleged measurable distance depend on certain sets of assumptions? Are there other sets of assumptions that can equally explain those measurable differences??
And no you see why I'm an agnostic. Most of those questions still await answers. Thus I leave the questions open.
