OK, so why 70 weeks? That is 70 x 7 or 490. This is the period of time for forgiveness. This applies to everyone, not just the Jews. Then on the 69th week the Messiah is cut off. That indicates that the sins and offenses people do escalate. This is like the drug addict who has to hit bottom before he will repent.
However, the gospel went to the four corners of the earth after Jerusalem was raised to the ground by Titus. The Romans celebrated that victory in 71 AD. 4 x 70 x 7 +71 = 2031. The period of time for people to repent runs out in 2031. But in the week before that, in the year that begins in 2025 they cut off the Messiah again, that which has been done is that which shall be done. Jesus told Saul of Tarsus why persecutest thou Me, talking about Saul persecuting the Body of Christ. So then, based on that prophecy we would expect a crucifixion to take place again, followed by the Lord's resurrection -- which will be the rapture. This will then give people seven final years to confess and repent before the opportunity to receive grace is fully gone.
This also explains the gap in time for the Jews. They rejected the Messiah, so they were put on hold as the Lord went to the Gentiles, brought salvation to the whole world. and then when we get to that 70th week for the whole world we also will see the Jews come to their 70th week. This will be the "second chance" to receive the Messiah. In the Bible there is a second Passover for those who missed the first one because they were defiled by a dead body. The Jews have been defiled by the dead religion that rejected Jesus and told them He was not the Messiah. So they get a second chance and that will also be true of all those who have been defiled by apostate religion and are left behind after the rapture.