Why did this pump break??

It looks to me like the bearing in the center of the wobble plate seized. If you turn the wobble plate does it turn the motor over?. The plate when detached from the diapgagm, should turn freely without turning the motor. The wobble plate is mounted on the motor shaft at a slight angle. As the motor turns it causes the wobble plate to wobble, which is how the diaphragms move back and forth. If the center bearing seizes, it turns the plate breaking the the support webbing as in your picture.

From the appearance of rust on the the bearing in the photo, it would appear that there was a small leak into the housing behind the diaphragm causing the seizure.