Even though Pompeii was a terrible event the people had a few days to escape. The city was mostly empty by the time the major eruption started and by then it was too late for the stragglers.
Most people don’t recall that neighboring ‘Herculaneum’ was allso wiped out.
“... the sighting of a column of smoke ... triggered a response more of curiosity than of alarm...”
“... there were warnings of the eruption of Vesuvius.”
https://www.bbc.co.uk/history/ancient/romans/pompeii_portents_01.shtml