Why does making a GameObject a Prefab give it a BoxCollider component?

When I take a game object with several children and drag it into the Resources folder to make it a prefab, why does Unity give it a BoxCollider component?

Is there a way to change this (default) behavior?

That’s not actually something that happens; Unity won’t add components unless you tell it to in some way. Maybe you have a script with RequireComponent(BoxCollider), or you just overlooked it. By the way, you make prefabs by either dragging them into the Project view, or by doing Create->Prefab and dragging onto it…the Resources folder isn’t involved.