Agnostic isnt even really a thing, in the sense people use it at least. Gnosticism deals with knowledge, theism deals with belief.
Agnostics dont know if there is a god. Atheists dont believe there is a god (and its worth noting thats not the same thing as believing there is no god, its just not believing in a god). So, given no one can KNOW, we technically are all agnostic (though some would surely declare god as a fact).
Asking the question do you believe in a god should be a yes or no question, because answering no doesnt mean youre positive there isnt a god. You either believe in a specific god or you dont. The misconception is that people think being atheist means you have absolutely ruled out with 100% certainty no god exists, which is just not the case.
If you dont specifically believe in a specific higher power, youre an atheist. People have conflated that word with being more hardline than it is.
People also don't want to be associated with some of the more annoying/outspoken atheists out there, so they figure agnostic is a safer label to use instead.
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Ah, yes, the Negotiator: General Kenobi <sneaky beeping>