I don’t understand why his organs were not usable by the time he died. This tells me they were only usable while he was alive....
Hmmm.
Because before actual brain death occurs, the body often deteriorates physiologically to the point where organs are no longer functional and cannot have functionality restored. For one thing, circulation and oxygenation can be severely impaired for quite some time before brain death, because the body will prioritize getting oxygen to the brain.
Sounds to me like his condition was deliberately allowed to deteriorate, so they could harvest the guy.