Drum brakes are cheaper to manufacture than disc brakes, because there are fewer moving parts and because in the rear the parking brakes (which often works by a Drum-and-shoe mechanism even on four-wheel-disc-equipped cars) can share a Drum with the “regular” brakes.
Drum brakes last longer because drum brakes have increased friction contact area than a disc. Drum brakes are cheaper to manufacture than disc brakes. Rear drum brakes generate lower heat. Drum brakes have a built-in self energizing effect that requires less input force (such as hydraulic pressure.