We come to those conclusions, if we're rational, through logical argumentation founded on strong evidence. Depending on the information we have, we will come to different conclusions even if we're both perfectly rational.
I tend to think, for a variety of reasons, that theists generally have good reasons for believing in God, even if I disagree with their conclusions. I don't know what those reasons are until I have that conversation with them. It's possible that their reasons for believing in God are superior to my reasons for believing that God does not exist.
I don't know if this is the place or if I'm going too far off a tangent but we need to discuss this sometime somewhere.
If logic is unambiguous and we both have the same information, we should come to the same conclusion. So, either logic isn't the right tool to deduce truth from true premises, or one of us is making logical errors if we come to different conclusions on the same premises.
Theists and philosophical Atheists can't be both rational if they claim their conclusion to be true. (I think they both are irrational.)
They may have reasons to
believe (i.e. subjectively assign a believability threshold to their premises) but that doesn't mean they
know.
And to get the bow back to the topic, lacktheists don't face that problem and are therefore (probably) right. There just isn't enough information to come to a rational conclusion. At least not enough to reach their threshold of believability.