In the first place a lightning rod does not protect a house unless the lower end is well buried in the ground. If the lower part of the rod is rusted and broken off at the ground it really attracts the lightning, and then discharges it into the house. Lightning is electricity. Metals attract and conduct, or carry electricity better than anything else does. So if lightning is discharged above a house it is easier for it to go to the metal rod and run down that, than it is to spread over the roof. But there is now less faith in the protective powers of a lightning rod than there once was, and fewer rods are used.