My understanding as to why this happens is because in a hospital when someone dies, what they write down in the death certificate is the actual and direct cause of the death not the event that caused the death. As if, someone falls from a 20th story building the cause of death will be “blunt force trauma” For the untrained medical person there is no possible way to relate a blunt force trauma to falling from a 20th story building.
In abortion, for example, if the procedure results in a perforation of the uterus, the perforation would probably cause a hemorraghe that can cause the death of the woman but because the direct cause of death was the hemorraghe, hemorraghe is what goes on the certificate, not abortion, making it then extremely difficult for anybody to identify who died from an abortion.