I've never asked why they do that. As a retired medic, there must be a medical reason. But, at least in the rural areas I worked, many dead people simply never get to the hospital. As a medic, I've called my share of dead people. When that happened, I would call dispatch and tell them there would be no transport to the hospital. And then law enforcement and the local funeral home would be dispatched to the scene. The cops had paperwork to do for county records and the funeral home would transport the dead. So unless the cops thought there was something that needed to be investigated, there would not be any autopsies done. The death certificate was done by the dead persons doctor as reviewed from medical records. Even I could give a good cause of death. In a small community, where you work on family and friends, I probably had already scraped you up a couple of times and was familiar with your illness.
And if a hospital sell them more than once, think of the pure profit!