Selfishness [1]
Tiamat and the Zara/Alea duo were unique, but not as unique as one would expect.
The way they reacted to the Dsrk God's energy was unique, and was the opportunity they gained from it.
However, they weren't the only ones it affected.
As mentioned before, the Dark God's energy spread to affect all three of the cosmos that were related to each other: the True Void Universe, Sacred Abyss Universe, and Sanctuary.
Why Tiamat sensed the energy was obvious, but what about Zara and Alea?
They had Nox blood, sure, but not all of the Nox were able to understand what had happened. In fact, aside from Yong An and a few others, none of them were affected in the slightest.
But when it came to the three involved cosmos, the number of people who were truly affected by the Dark God's actions was uncountable.