When the war comes and the city is bombed, Montag has a horrible vision of Mildred still standing in her TV parlor, living with her "family" without knowledge or care for her impending death.
He saw her in her hotel room somewhere now in the half-second remaining with the bombs a yard, a foot, an inch from her building. He saw her leaning toward the great shimmering walls of colour and motion where the family talked and talked and talked to her, where the family prattled and chatted and said her name and smiled at herand said nothing of the bomb...
(Bradbury, Fahrenheit 451, Google Books)
This reaction, it is implied, is repeated by people all over the city, people who are so obsessed with their meaningless entertainment that they have paid no attention to the growing concern of war. News and politics are of less interest to them than their own instant gratification, and so they are not worried about the bombs. After all, if it doesn't happen on the television screens, it isn't real. Some people leave the city, but the vast majority remain, content in their bubbles of personalized television. Without someone telling them what to think and how to process information, they had no way of realizing that the impending war was actually real and actually a threat to their own lives.