Here's why:

* Angular momentum is a measure of an object's tendency to rotate. It depends on the object's mass, its velocity, and its distance from the axis of rotation.

* Linear motion involves movement in a straight line. There is no rotation involved, and therefore no axis of rotation.

Example:

Imagine a car moving in a straight line. It has linear momentum because it has mass and velocity. However, it does not have angular momentum because it's not rotating.

Key takeaway:

Linear motion and angular momentum are separate concepts. An object can have linear momentum without having angular momentum.