Why are there so many atheists compared to agnostics?

I am curious as to why so many people are atheists (in comparison to agnostics). In my opinion, believing that no god or deity exists is almost as silly as believing that they do exist. Both cases lack tangible evidence. Is it because those atheists are actually agnostic but do not know the differences? It's quite ironic, actually, to think that atheists, who disregard religions due to lack of evidence, hold a stance that has no evidence or proof.