Magnetic brakes don’t work well at low speeds. You need the metal to be experiencing a sudden change in magnetic fields for it to generate strong enough eddy currents to push back with much force, otherwise you’d need a large area or number of field changes to generate useful force. This means you’d still need your friction brakes to slow you down from most slower speeds in which case why add complex magnetic brakes? You still need rotors, calipers, and pads but now you need ferrous rotors and a magnetic field generator **and** your stopping force is still limited by the tires grip on the road
The one good application for magnetic brakes is trains. They have Eddy Current Brakes which help slow the train down. Trains have the ability to have a lot of eddy current brakes to help make up for the poor traction between the wheels and the rails, and since the rails are already ferrous nothing needed to change, it was just a straight improvement in the stopping power of trains because the magnets gave a second path for braking force to be applied rather than just through the already overloaded wheel/rail contact surface.
It’s called regenerative braking, and it’s used in electric and hybrid vehicles. The electric motor can also act as a generator, recharging the battery. This causes eddy currents that can provide a lot of braking resistance. You don’t want to rely on this to stop a car, because it can’t. The slower you go, the weaker the effect, so you still need a clamping force to bring the car to a complete stop.
One thing that comes to mind is that friction brakes still work even when the vehicle is completely off. Run out of fuel? Battery died? You can still stop the vehicle.
That being said, many electric and hybrid cars do use magnetic braking to help recharge the battery, but they still have physical brakes as well.