Eagle-Talk (Preparing for Episode 4!)

Magnetic braking is strongest at high speeds, so it's great for slowing things down but not so good at stopping them. You would need some additional system to, for instance, hold a car still while it is on a slope. And if that additional system works perfectly well at all the operational speeds of the car, why put in the magnetic braking in the first place?

That said, a lot of electric cars do use magnetic braking along with friction brakes, because the eddy currents in the brake plate can be used to recharge the car's battery somewhat. This is the basis for regenerative braking.