Read the rest of it. Jesus was applying his revelation as Messsiah and Judge in the more immediately context, if not also in the eschatological context. What he was saying is that he had come not just to bring salvation, but also to bring judgment, though that judgment was tempered in some respects. Israel, who had been given the knowledge of God, would suffer devastating destruction, whereas pagan nations, like Rome, would be given opportunity to enter into Israel's covenant relationship with God.
Luke 17.28 “It was the same in the days of Lot. People were eating and drinking, buying and selling, planting and building. 29 But the day Lot left Sodom, fire and sulfur rained down from heaven and destroyed them all.
30 “It will be just like this on the day the Son of Man is revealed. 31 On that day no one who is on the housetop, with possessions inside, should go down to get them. Likewise, no one in the field should go back for anything. 32 Remember Lot’s wife! 33 Whoever tries to keep their life will lose it, and whoever loses their life will preserve it. 34 I tell you, on that night two people will be in one bed; one will be taken and the other left. 35 Two women will be grinding grain together; one will be taken and the other left.
Jesus was saying that his 1st Coming was a revelation that in a day would bring about the destruction of Jerusalem and the temple, via the Roman Army. It would also come at the end of the age, to judge the world, but more immediately it would bring devastation to Israel, in view of Dan 9, where it was written that "the people of the ruler to come would destroy the city and the sanctuary."
This was the destruction of Jerusalem and the temple, Israel's form of worship. Their covenant was broken, and God would show that it was broken by completely destroying the temple, the symbol of that covenant.
But this was not an annihilation of the people, a genocide, as it had been in Sodom and Gomorrah. No, Jesus was referring to the total destruction of Jewish independence and religion in Jerusalem. Consequently, Jesus' appearance at the end of the age would bring great judgment, as well. But it would not annihilate the world. If God did not annihilate Jerusalem in 70 AD, then neither will He annihilate the world when Jesus comes again.
In case you don't understand, the passage above speaks of a time that is limited to Jesus' time in history, when people came down from their roofs in Jerusalem. The Romans took some away into exile, and left others, to work the fields for them. This was hardly an annihilation, even though Jesus compared the judgment to Sodom, which was equally devastating.