Because it is a fatality directly related to the seizure. The reason being more money is spent on research and better treatment and medication as well as social programs. As it is now because 80% of persons with seizure disorders are effectively treated more money isn't being spent to help the 20%. Many causes such as choking to death, heart failure, sudden unexplained death, the list goes on are directly caused by the seizure but not recognized as so.
It is a life threatening illness that many people do not realize. The medications used to control them can be life threatening and can cause other illnesses such as Lupus. Some have success in controlling the seizures for an aproximation of 7 years and then the meds become ineffective. It's things like this that are still unknown so there are still a lot of cases where it's untreatable.
Granted, much more is known and better meds than 20 years ago but the remaining percentage still suffer and it isn't enough to motivate the drug companies to continue to develope better medication.
Would he have fell in the pool and drowned if he hadn't had a seizure? The guy that fell into the subway that was saved?
ETA: Just wanted to clarify that my position initially stated in my post was for a compromise so that the cause is more accurately recorded such as drowning/seizure so it is made known that's what happened. It's only fair.