It is a universal tribulation.
Matthew is speaking directly to the Jews, being a Gospel to the Jews.
In Luke, the Gospel to the Gentiles, we find the universal nature of the Tribulation.
And there shall be signs in the sun and in the moon, and in the stars, and upon the earth distress of nations, with perplexity; the sea and waves roaring. Men's hearts shall failing them for fear, and for looking after those things which are coming on the earth, for the powers of earth heaven shall be shaken. (Lk.21:25-26)
In Luke, the Gospel to the Gentiles ...
Where does that come from? Seven
In Luke, the Gospel to the Gentiles, we find the universal nature of the Tribulation.
This certainly explains why differ language would be used to describe the same event. But it does not explain why most of the language in both passage is localized to Judea.
A reasonable conclusion is that it refers to the localized events surrounding destruction of the temple in AD70. (The universal sounding language here is explained by a careful comparison with OT prophetic language.) Matthew pictures it in language that would be recognizable by a Jew, while Luke speaks in words more suitable for a gentile audience. But they both describe ancient Rome -- Daniel's fourth kingdom which was eventually replaced by the eternal kingdom of Christ and His saints (Dan. 7:27) -- marching againt Jerusalem. "Then let those who are in Judea flee to the mountains, let those who are in the midst of her depart, and let not those who are in the country enter her" (Luke 21:21).
No one has yet been able to explain why, if this is worldwide tribulation in view, that folks in one tiny part of the world are told to "flee to the mountains". Why no mention of the mountains in, say, Colorado?
No one also has explained why, after having these warnings from Jesus for 2000 years, that still in the futurist "great tribulation" holocaust that two-thirds of the Jews living in Israel still be exterminated. It wouldn't be a big deal for a bunch of believers to go into Israel and put up billboards around Jeruaslem saying:
Jesus to Israel: "But when you see Jerusalem surrounded by armies, then know that its desolation is near. Then let those who are in Judea flee to the mountains, let those who are in the midst of her depart, and let not those who are in the country enter her."Perhaps you could replace the phrase "surrounded by armies" with "abomination of desolation", but I'm not sure how many of them would get it.
And since even armed soldiers like the Taliban were not able to make effect use of the mountains in Afghanistan for protection from invading armies, why would it be safe for unarmed folks in a future universal conflagration to flee in such a fashion?
Not everyone accepts the conclusion that it is the same narrative being spoken by Jesus, even though that fact is quite clear, and all signs point to AD70.