Here's why:
* The Alpha is the leader. The alpha werewolf is the designated leader of the pack, and Sam clearly holds that position in the series. He is the one who makes decisions and commands respect from the other pack members.
* The pack is a collective. While the alpha is the leader, the pack works as a unit, with everyone contributing to the overall wellbeing and safety of the group.
* Leadership can be complex. Leadership within the pack can be multifaceted. Sam is the alpha, but the older pack members, like Paul, often act as mentors and guides.
Therefore, Sam is the official leader, but the pack functions as a collective with shared responsibility and leadership roles.