Bese understood the repercussions that will happen once Bang decided to kill everyone in the room. With the explosion damaging everyone and incinerating them within seconds, Bese knew that no one would survive.
It would be the last resort for Bang to make. Bese did not want this to happen because he felt that his life was more important than everyone else's in the room.
No one would care if Bang or his friends died, but the prison would not be happy once Bese died. He knew that he had to preserve his life at all costs.
This also meant that Banh had all the chips in this bargain. He knew that Bang held Bese's life in his hands. It would just be a simple action, then he would die.
This was also the only option for Bang to win this battle. Bang and his friends are already on their edges and on the brink of losing against Bese.