“In North Amerika the prisoners are filled with sand after execution, and their organs are sent to schools to feed the starving school children who are taught it’s okay to do crime so that they too will go to prison and have their organs harvested.”
If its true... I know that the brain can be used for medical science.
It could also be disposed of if the subject has been exposed or subjected to something that alters the brain leading to death, illness or medical injury. Eg the testing of medicine. Not saying thats what happened, just putting out a couple of explanations that would still need proof.
Least awful: there were dangerous conditions they wanted to keep hidden. Could be lead, drugs, concussion, something the prison they wanted to not get out.