A good question. Because according to biblical prophecy, the return of the lost tribes of Israel signals the coming of the Messianic Kingdom. And when Christ came, He restored Israel by freeing the captivity from spiritual babylon, and brought the lost sheep of Israel home. For this anti-type to take place (Matthew 12:29), the type had to have taken place (Jeremiah 50:4-6). The lost of Israel had to be delivered from bondage and restored.
so says Tony Warren of mountain retreat
He goes on to the conclusion that: Ephesians 4:8
* "Wherefore he saith, When he ascended up on high, he led captivity captive, and gave gifts unto men."
The Gift which is Salvation, freedom from bondage to Satan, freedom from serving sin, restoration of the Kingdom to Israel by the making of Christ to ascend on High, a King, reconciling the lost sheep of the house of Israel to God. The fulfillment of the prophesy of the eternal restored Kingdom, which has no end.