It has nothing to do with passiveness, not at all.
It's a function of standard language.
You can assert gnostic atheists are believers in a religious mindset, but not an agnostic atheist.
Agnostic atheists may discuss, debate, lecture, etc etc etc... but it's more dissertation and expression of thoughts than a belief-based diatribe.
Most such atheists would say "praise God!" if such a being delivered itself right in front of us. It's hard to dispute pure evidence if its available.
The evidence the vocal atheists see today supports our/their arguments, and thus that establishes the basis of conversations and research. Many are like-minded due to the simple fact that one key piece is shared: they have arrived at the same conclusion, that empirical evidence today strongly asserts the notion that God does not, and has not existed. So, they share that, discuss it, use it to feed off each other's thoughts and even debate one another if contrary points are discovered.