First of all, the phrase is "all the tribes of the land". Not the whole Earth. The use of the word "tribes" should make us think of the tribes of Israel. This is according to Biblical usage.
If you recognize that Revelation and the Olivet Discourse are apocalyptic literature then it is reasonable to compare it with the apocalyptic portions of the Old Testament. Fair enough? And in those Old Testament passages we have stars falling, hills melting with blood, much of the same imagery we have in similar NT passages.
"They shall see the Son of Man coming in the clouds of heaven with power and great glory". Yes, certainly. It is not an invisible coming. But who are the "they"? It is still in the context of "this generation" - "this evil generation" (more on this point below).
Anyone who is familiar with Josephus' account knows this is exactly what happened:
"Besides these, a few days after that feast, … a certain prodigious and incredible phenomenon appeared: I suppose the account of it would seem to be a fable; were it not related by those that saw it; and were not the events that followed it of so considerable a nature as to deserve such signals. For, before sun setting, chariots and troops of soldiers in their armour were seen running about among the clouds, and surrounding of cities. Moreover, at that feast which we call Pentecost; as the priests were going by night into the inner temple, as their custom was, to perform their sacred ministrations, they said, that in the first place they felt a quaking, and heard a great noise: and after that they heard a sound, as of a multitude, saying, “Let us remove hence.”
Sepher Yosippon relates this:
"...Now it happened after this that there was seen from above over the Holy of Holies for the whole night the outline of a man's face, the like of whose beauty had never been seen in all the land, and his appearance was quite awesome. Moreover, in those days were seen chariots of fire and horsemen, a great force flying across the sky near to the ground coming against Jerusalem and all the land of Judah, all of them horses of fire and riders of fire."
Similar comments are from Tacitus, Suetonius, and others.
So, yes, it was seen.
It was not seen over all the Earth because it did not have to do with all the Earth.
It did not involve all the ages because it had to do specifically with "this generation".
Speaking of "this generation"...
Instead of trying to explain again concerning the use of that phrase in Matt. 24 it may be helpful to examine the phrase in other passages:
1."Then certain of the scribes and of the Pharisees answered, saying, Master, we would see a sign from thee. But he answered and said unto them, An evil and adulterous generation seeketh after a sign: and there shall no sign be given unto it, but the sign of the prophet Jonas: for as Jonas was three days and three nights in the whale’s belly, so shall the Son of man be three days and three nights in the heart of the earth. The men of Nineveh shall rise in the judgment with this generation, and shall condemn it, because they repented at the preaching of Jonas and, behold, a greater than Jonas is here." - Matt. 12:38-46: (compare Luke 11:16, 24-36)
2. 'For the Son of man shall come in the glory of his Father with his angels; and then he shall reward every man according to his works.
'Verily I say unto you, there be some standing here, which shall not taste of death, till they see the Son of man coming in his kingdom.' - Matt. 16:27, 28
3. "Woe unto you, scribes and Pharisees, hypocrites! because ye build the tombs of the prophets, and garnish the sepulchres of the righteous, and say, If we had been in the days of our fathers, we would not have been partakers with them in the blood of the prophets.
Wherefore ye be witnesses unto yourselves, that ye are the children of them which killed the prophets. Fill ye up then the measure of your fathers. Ye serpents, ye generation of vipers, how can ye escape the damnation of hell?
Wherefore, behold, I send unto you prophets, and wise men, and scribes: and some of them ye shall kill and crucify; and some of them shall ye scourge in your synagogues, and persecute them from city to city: That upon you may come all the righteous blood shed upon the earth, from the blood of righteous Abel unto the blood of Zacharias son of Barachias, whom ye slew between the temple and the altar. (Compare Rev. 16:6, 17:6)
Verily, I say unto you, All these things shall come upon this generation." - Matt. 23:29-36 (Note: this is the same phrase used in the end of the Olivet chapter, Matt. 24:32-34)
Luke has it:
"verily I say unto you, It shall be required of this generation.'"
I hope you can see that the examples above relate to a specific generation - the ones who were living in the 1st century.
The idea that the phrase "this generation" refers to that first century is not just a preterist belief. The following authors are not preterist:
"The King left his followers in no doubt as to when these things should happen: ‘Verily I say unto you, this generation shall not pass till all these things be fulfilled.’ It was just about the ordinary limit of a generation when the Roman armies compassed Jerusalem, whose measure of iniquity was then full, and overflowed in misery, agony, distress, and bloodshed such as the world never saw before or since. Jesus was a true Prophet; everything that he foretold was literally fulfilled." - C.H. Spurgeon (1868): The Gospel of the Kingdom, p.218
"The phrase ‘this generation’ is found too often on Jesus' lips in this literal sense for us to suppose that it suddenly takes on a different meaning in the saying we are now examining. Moreover, if the generation of the end-time had been intended, 'that generation' would have been a more natural way of referring to it than 'this generation.’” - F.F. Bruce (1983): “The Hard Sayings of Jesus,” p. 227