If there is no God, then what is the meaning of life? Maybe what God supposedly wants or plans is just as unimportant as the possibility of being run over by Santa Claus or being kidnapped by the color green. But this does not diminish the meaning of life. Giving gifts is just as meaningful as ever, even though I don't believe in Santa Claus.
Why am I here? Why do I exist? Atheism has no answer only because the question assumes there must be a reason envisioned by some purposeful God.
It's not a limitation of atheism. The question is similar to "When did you stop beating your spouse?" assuming that the person being addressed has been beating their spouse. If they never beat their spouse, then technically they simply cannot answer the question. (52. Jerome Shaffer, Reality, Knowledge and Values (New York: Random House, 1971), pages 104-105.)
The theist must prove the existence of God. The theist offers an explanation of existence and must give reasons for accepting it. This also applies to the most basic assumptions of atheism, but more about that later.
If the reasoning for belief in God is faulty, then it can't support the claim that God exists. Ignorance of alternative explanations doesn't justify belief in God. Only knowledge justifies beliefs, not ignorance. We cannot cannot merely assume what we're trying to prove. And because we have to start with premises, it is impossible to prove God's existence.
So there is good evidence against the existence of God, generally as a good creator and specifically as in an ultimate personal mind.