Every generation is tasked with a unique mission and is given the powers needed to accomplish it. We are working through the world and refining it. Once we are done= Geula.
Yeridas hadoros is because each generation had an easier / lower mission to work on than the generation before so they get progressively weaker as well, as our power matches our mission.
For example, the generations of the Tannaim and AmoraiMy were tasked with refining the intellect of the world’s. They were brilliant, and the nations of the world were as well. That was the time of philosophy.
Contrast that for today and no one cares for Aristotle…
Since we don’t need to refine the wisdom of the world anymore, we are lacking in the wisdom they had… There is alot more to be said but here’s for starters.