Deadly staircase
The people who had come out were ready to risk their lives. It had taken all of their will to muster up the strength to come out here to fight against the zombies. Some of them had even bid their last farewell to their loved ones, including children, older relatives and significant others.
The sheer sound outside gave them an idea of how many zombies were coming towards them, and based on the worried look on the faces of those they had relied on so far, their chances didn't look hopeful. In the end, there was one person who had convinced them.
Seeing Ryan risk his life so confidently, they felt guilty, extremely guilty that someone else would be fighting on their behalf while they sat inside and did nothing. In the end, if they didn't come out to help Ryan and others to fight back against the zombie herd, it would only hasten the inevitable.