Why do you think people do not talk about the recent blackout like they do with the rest?

In chapter 6, the latest power failure is said to have lasted seven minutes. This is twice as long as the previous ones.
No one talks about the recent blackout, however. In the past, power failures always generated local gossip and loud discussions about incompetence of city workers. This time, the whole city is quiet, and residents refuse to openly discuss the blackouts. The main reason for this is because Ember's citizens are afraid that the failing generators and eroding supplies will eventually lead to the city's destruction.
Basically, everyone is afraid that they could die if things don't change. To underline the seriousness of the situation, Mayor Cole calls for a town meeting in Harken Square the next day. However, things get out of hand during the meeting. The Mayor is barely able to make himself understood through the megaphone. He tells the crowd to be patient and to trust that solutions will be found to address the crisis at hand. However, the people are tired of being placated with empty words. They become angry and begin throwing things at the Mayor. It is their deep-seated fear that motivates their anger.
So, no one talks about the recent blackout initially because they are all afraid that the city is doomed to destruction. During the town meeting, however, the people's emotions boil over, and they begin to demonstrate their true feelings about the current crisis.