How was it that the End Times were (broadly) predictable so long ago? Why was it clear that evil would (sooner or later) prevail in this world?
The basic reason could be that the demonic powers are immortal spirits while Men are mortal. And this was, of course, a fact well known to our ancestors - who drew conclusions that were, perhaps, much clearer and more obvious (at least, to the more thoughtful and insightful among them) then they are nowadays.
This fundamental asymmetry means that evil is able to plan and scheme on a timescale across the whole history of the earth and multiple human generations; whereas, by contrast, each human generation must (in a sense) start afresh with learning about the world.
Thus, the demons tend cumulatively to out-strategize Men.
Another ways of thinking about it is that this mortal world is ruled by entropy. Although we are created-creatures in a created-world, and God is still create-ing; nonetheless we are mortal incarnates, and entropy must win-out eventually.
Over time, entropy will overwhelm mortal creations.
However; evil spirits are excluded from Heaven; and in Heaven, Men are eternal incarnates: There is all-creation and no entropy.
Therefore, as this mortal earth wears-down, the odds increasingly favour evil; and the End Times were always inevitable.
But in Heaven... well, there things are very different.