1. Why do cars even have differentials?

There are no cars that don’t have differentials in them—otherwise we would be driving through tight curves with the wheels spinning and tires screeching. This essential component is located in the center of the drive axle, where its function is to make sure that the two wheels can turn at different speeds when driving around curves, while nonetheless having exactly the same propulsive power. The torque of the motor is always divided in a fixed ratio.
By the way: All-wheel drive vehicles have a differential on each axle, plus a central differential that distributes the engine power between the axles in a given ratio.