[masraum]

Because there are always loses in the system

If you put a fan on top of the car, it would cause drag which would require more power

As stated an alternator requires power to spin (it's not as easy to spin when it's in the car making electric as it is when it's in you hand)

Perpetual motion is impossible

They do have reclamation systems in most/some of them

When they hit the brakes, most of them are generating electricity