You seem to imagine that expectation is supposed to guarantee fulfilment. People wrote stuff that they thought would happen after other stuff happened. The superstitious claims about what would supposedly follow the destruction of Jerusalem simply didn’t happen (though Revelation, written later, does also allude to some events during the reigns of individuals such as Domitian that aren’t included in the ‘gospels’). The NT claims about tribulation contai a mixture of mundane statements, hyperbole and fantasy, none of which means that any of it is legitimately ‘prophetic’.
(Also, comparison of Luke 21:25 with Matthew 24:29 and Mark 13:24 shows that even in the story, the ‘signs in heaven’ follow the tribulation.)