Agnosticism stops at the question of whether there can be knowledge about whether a deity exists. For an agnostic, presumably the answer is "no," but there is no conclusion drawn from that about how we live our lives.
In some ways, your typical atheist are even more agnostic than agnostics are. In most cases, they aren't trying to answer the question of whether it is possible to have knowledge of deities. They are only assessing the current evidence that exists. And for an atheist, the answer to that is "none." In addition, it usually includes a component of practical philosophy: if there is presently no reason to believe something exists, then we should not factor it into our assessment of the reality we live in until such a time as there is.
This is why there is such a thing as an "agnostic atheist," but not such a thing as an "atheist agnostic."
Agnosticism is mostly addressing a question of the limits of knowledge. Atheism is mostly addressing practical philosophy for living.