There is a very good reason, Paul, an apostle, called the times, the epoch, the era, that we are living in THIS EVIL AGE
The governments of the world, the banking system, the true "power brokers" behind the scenes, the whole thing is in the power of the Evil One. He said, it and Yeshua did not argue the point. "The fullness of the gentiles", is actually when the evil that the gentile nations are capable of reaches its full height. (The parallel is the fullness of the sin of the Amalekites in the books of Exodus, Deuteronomy and 1st Samuel.)
We take it to mean until the full number of gentiles is saved, because we live and breathe a self-centered, gentile-centered gospel that has nothing to do with the foundation of God. Israel is the center of the story, what they experienced in there long journey with the God of Israel is there for us to learn from and continue to apply. God is a covenant-keeping God. He will complete His purposes in and through THEM. We are brought into their promises by the grace and mercy of God to include the nations who had been given over to the false gods they chose. We come in as individuals, they will come in as an all-saved nation.
The God of Israel is patient, no one can say He is not.