They'll be able to see the road in front of you is clear and you have no reason to stop. Part of their training is to maintain a steady constant speed and avoid unnecessary braking, so they'll gently ease off instead.
That's precisely the point. They don't ease off. They catch up and then drive too close mile after mile. Seeing that the traffic in front is moving is no defense if something unexpected happens causing people to brake resulting in a collision because they didn't leave a safe gap. My normal response is to gradually let my speed drop to the mid to low 40s so they get fed up and move to lane two and tailgate someone else.