Why did sherif's participants change their estimates when they had to call out their answers in the presence of other people?

The participant's changed their answers to conform to the group standard

Every individuals have the inner fear of being outcasted by the other members of a social group.
To avoid this, most people develop the tendency to conform to a group's opinion even if they personally believed in different things.
One of the most known studies that first introduced this tendency to the world is called  Asch conformity experiments