These 8 traits seem to focus on working with other. Being able to build relationships, communicate, build a team, and the other traits involve working with other people and serving other people in order to be a successful leader.
I agree that these traits all have a common factor of working with others. It would be extremely hard for a person to try and lead a group of people without being able to communicate with others. In order to be a leader, a person must have followers to actually lead. Without good people skills, it would be very hard for a person to encourage others to follow them.