Here's why:

* Static friction is the force that opposes the initiation of motion. It's the friction that keeps an object at rest.

* Kinetic friction is the force that opposes the motion of an object that is already moving.

To keep an object moving at a constant speed, you need to overcome kinetic friction, not static friction. This is because once the object is moving, static friction is no longer acting on it.

Think of it this way:

* Static friction: The force you need to overcome to get a heavy box to start sliding across the floor.

* Kinetic friction: The force you need to keep pushing on the box to maintain its speed while it's already sliding.