At one time these people may have attempted to encourage each other to live. Eventually they lose hope. The essential dynamic of a suicide pact is that the pain and fear of living becomes worse than the fear of dying. Suicide is not an easy decision. Nobody wants to die alone.
Suicidal people can encourage each other in their suicidal behavior.
A suicide plan that involve a public display develops out of a motivation to give death a sense of purpose and meaning. A public suicide is usually intended to send a message, inflict emotional harm and to punish others. A suicide following violent behavior is intended to escape responsibility and accountability. Strangely, such suicide are a means for people to stay in control and to make their own choices. People who tried to support each other in life now support and encourage each other to support each other in suicidal and other violent behavior.