Here's why:

* Centripetal acceleration is always directed towards the center of the circle. This is what keeps an object moving in a circular path instead of flying off in a straight line.

* Tangential acceleration is a component of acceleration that is parallel to the velocity of the object. This would cause a change in the object's speed, not its direction.

While an object moving in a circle might experience a change in speed, the key defining characteristic of circular motion is the constant change in direction due to the inward centripetal acceleration.