Let me say that regarding Luke, it dealt with the 70AD seige of Jerusalem in vs. 20-24.
Verses 25-28 deal with future events.
Verse 25 speaks of the earth and nations, hence the universal nature of the tribulation.
As for why many Jews do not believe what is going to happen (as do many Gentiles and Christians), it is because of deception and disbelief in what the Bible says (2Pe.3:3-4).
No doubt that most Jews had given up on the coming Messiah also,but he came, just as the prophets predicted, but not like the interpetators thought.
They did not know that Christ had been born in Bethlehem but lived in Nazareth (Jn.7:42 cf 52).
Just as the 1st advent prophecies were literally fulfilled, so will be the 2nd.
Verses 25-28 deal with future events.
Verse 25 speaks of the earth and nations, hence the universal nature of the tribulation.
The exact same breakdown is found in Matthew. First a description of local judgment where Jesus speaks to them in first person plural, "But when you see Jerusalem surrounded by armies" and "they they will lay their hands on you and persecute you, delivering you up to the synagogues and prisons. You will be brought before kings and rulers for My name's sake". It speaks of all these things coming upon "this generation".
The only difference is that Luke uses gentile language and Matthew uses Hebrew language.
Some take the view that Luke and Matthew are speaking of two entirely accounts. But we know that cannot be the case. So the only question is where in the account is the transition from the local (AD70s Judea) to the universal (the future second coming? I think the break is in Matthew 24:36, "But of that day and hour no one knows, not even the angels of heaven, but My Father only. But as the days of Noah were, so also will the coming of the Son of Man be." Jesus goes from giving very detailed information about the destruction of the temple that would come upon this generation, even telling those in Judea to "flee to the mountains" when they saw the abomination of desolation/Jerusalem surrounded by armies event. That would be the last time element in order to be saved.
But in vv. 36 and following Jesus' description radically changes. Of this event, His second coming, He says that no one will know the time. Men will be going about their normal activities, even Christians. They will be marrying and given in marriage. Then, suddenly, one will be taken and another left. No time to flee to the mountains here. In fact there is no reason to think one should flee tot he mountains. Entirely different scenario being described.