Isn’t the purpose of lightning protection to prevent lightning from striking?

Nothing can prevent lightning from striking. If lightning is zeroed in on a particular object it will strike that object regardless of anything that is on the ground. The purpose of lightning protection is to intercept the lightning strike and carry it to ground. This is accomplished by placing the rods at regular intervals on all of the highest and most exposed parts of a structure. These rods become the most likely point for the lightning streamer to attach, since they represent the shortest path to ground. The rods are connected by a network of highly conductive cables that provide a low-resistance path to ground.