I don't fully understand how a sacrificial anode works, beyond the basics. Wouldn't each body panel need one? They must also be replaced regularly from my under

I don't fully understand how a sacrificial anode works, beyond the basics. Wouldn't each body panel need one? They must also be replaced regularly from my understanding. It seems like it would have been easier for Tesla to just coat the metal from the factory... or include the wrap in the price of the vehicle.