That patient died shortly thereafter. The condition is critical and there's a lot of immunological pressure put on the patient.
China is smart to study this in living cadavers first. It's much easier to find patients that aren't already on death's door, and there is no need to keep the patient alive. You can run experiment after experiment.
You can try a novel treatment on those but at the same time are limited by ethical concerns regarding pain and future survival (if the transplant "works", you are now in a tricky situation, as you can't easily do anything that has the potential to make the situation worse... and given it's uncharted territory, anything has the potential to make it worse).
Brain-dead people don't have such limitations. You don't have to worry about causing pain nor shortening potential survival, so you can try things that are likely to "kill" them (cause the transplant to fail, or other issues) and learn from the outcomes.
Fortunately determining brain death is a problem with a clear-cut answer with a clear line dividing “brain death” and “not brain death”. Right?