Cracks and other defects weaken the integrity of the device and also any connection. You see that crack in the face, god only knows what else has broken inside the receptacle's plastic housing.
Parts inside that should not be touching could come into contact with each other....just because some little piece of plastic inside that you can't see has probably broken off.
I've had old receptacles come out in pieces from boxes....not pretty.
First comes the round face usually still glued to the painted-over faceplate...then the two pieces of brass contact...followed by pieces of the rear housing that you have to use your fingers to sweep out of the device box.