Q:  The destruction of the Temple is dated 70Ad so why isn't this mentioned in the NT?

A:  YaHshua said that the Temple would be destroyed, in fact, prophecy was very specific -- not one stone on top of another.

The construction of the Temple and the walls surrounding it were massive.  The stones used in constructing the Temple and the temple compound looked as if set for eternity.  The Disciples were amazed at the work of men and the majesty and the massiveness of the construction. YaHshua, however, knew what was to come, and told them they were looking as something that was not immortal, and was not going to be left standing. To them, at the time, that would have seemed impossible.  Of course, the reality of history prove our Savior, YaHshua's, words would prove to be true.  The book of Josephus, gives a detailed account about how the Roman Army dismantled the Temple, stone by stone.  Many of the stones, over time, would be broken up, or recut and transported to other construction projects.  Today the Temple is gone, only a portion of the wall surrounding the Temple compound remains standing.  Josephus records that that portion of the wall was left in place just so that those who would come later could see what a miracle he and his forces had preformed in taking such complex piece of Jewish architecture down -- as a testimony to Roman might.

It is a matter of historical record that the assault on the Jewish capital, Jerusalem and the Temple Mount, began 68 AD and by late 70 AD, after nearly 3 years, the city walls and the Temple proper were breached.  There are wild estimates about how many Jews died, anywhere from a million to three million, but it is a fact that those who survived this rebellion against Rome were taken away to be sold into slave work camps or as slaves on the open market throughout the surrounding countries, including Rome.  

All of this, as a little background filler, to understand the question being asked and to see a possible answer, or not.  

Not one Gospel Book records the prophetic destruction of the Temple.  This would suggest that the Gospel messages and the Letters to the Churches from the Aposltes had not happened yet.  This automatically gives us dates for all of the Letters and the Gospels to have been penned before 68 AD.  Certainly, had one of the Apostles been around to witness this historical event, and event that our Lord and Savior, YaHshua, had predicted, it would have been written about.  Some one in the Faith would have bragged about it, right?  But, no, not one.  Now, that brings us to the Book of Revelation.

The popular consensus is that the Book of Revelation -- a book of revealing -- was written around 95 AD.  There is a huge problem with that dating.  It would mean that John, the author who penned the words given to him by his Savior, YaHshua, would have been a witness to those events.  He is writing a message to the Seven Churches located in Turkey.  Those Seven Churches are right in the path of the Roman Military, traveling to and from Jerusalem and Rome.  Also, long the coastal area are many shipping ports. John, himself, says that he is on the Island of Patmos, apparently under guard, but for whatever offense we do not know.

Nowhere does John, Identifying himself as a Servant of YaHshua, say or mention anything about the Temple.  Headline news would have been the destruction of the Temple.  John clearly tell us to whom this message is going -- the Seven Churches in Asia.  They are the principle audience. We can get a better timing of this writing, I believe, by letting the word tell us.  Remember, most in the Christian community and prophecy teacher have settle on 95 AD, but is this right, or only a wishful guess?

The Apostle John identifies the timing for us.  In Tribulation, and when was it that these Seven Churches were under tribulation and persecutions?  During the end rule of Nero.  Nero is famous for using the believers in this Messiah YaHshua as a scape goat for some of his own administrative failure, some say even for trying to burn Rome down, but that is all conjecture and no proof -- for example, Nero is said to have fiddled while Rome Burned, but the fiddle was not invented until some time after the 13th century.  Nero is also said to have lined the streets with Christians impaled on stakes and lit on fire, yet there is very little proof for this as well.  It seems his enemies were quick to start rumor mills against him and blame him for just about everything under the sun.  Sound familiar? Nero eventually became so depressed by all of the personal attacks and the death of his much loved wife that he took his own life, having served as Emperor for less than 6 years.  Want more info about Nero?  Learn how this was not the birth name of this Emperor, and how short his reign really was, and how he was a victim, in many ways, about the rumors and lies spread about him by his enemies.   A Source, check it out:  https://en.wikipedia.org/wiki/Nero

However, is it around this period, just prior to 68 AD that persecutions did happen, against the Christians.  Nero apparently ended his life in the same year Jerusalem was under siege by the Roman Army, so a change of power had taken place.  It is this period, it would seem, that the Apostle John alludes to.  John also menions the reason for his banishment to the Island of Patmos -- For the Word of God and the Testimony of YaHshua as the Anointed.  

Any time before 68 AD, then, would be the time period the Book of Revelation would have been penned.  The Temple would have still been standing.  What this timing does, is to destroy some popular teachings from the Evangelical and the Rapture people who center their understanding around the Escape doctrine, called, the Rapture.  

Why is the date 95 AD important to them?  So that their prophets can apply some important words about the coming of the Beast to a much later time and not have it applied to Nero or any of those who followed him. By putting the prophetic remarks out to be applied to a further date into the future, they need to void Nero out of the equation.  By this they make it impossible for John to be recording any prophecy about Nero or any other in a time period before the Temple is destroyed.  By putting it 30 years after that historical event, they are free to apply some of the prophetic word to their own desired views.  

We should, in my opinion, read the Book of Revelation as a Book of Revealing that has its beginning BEFORE 68 AD.  This is the only reasonable dating for this book.  John give us the approximate timing -- a time when there were 7 distinct Christian Churches located in Asia Minor, what is today known as Turkey.   These 7 cities were undergoing persecution, which John mentions.  These 7 cites, as Christian communities no longer exist, so, by the fact that they did exist then, during a time of Christian persecution and the absence of any mention about the extreme assault Jerusalem was to suffer, which would have to have been on the minds of every believer, far and near, at the time that happened, yet not one word.  And, this, then, would have an influence on the First parts of the future revelations John would write about.  Nero would still be in power, the persecution of the Christians, by the Gentiles, would have started, and the Temple and Jerusalem would still be in full swing, as the Jews would continue being a thorn in the side of Roman authority.  

The Book of Revelation must have been written before 70 AD, 68 AD might be a better date, before the Roman forces, marched on Jerusalem.