I think they are mostly concerned with two things: the PR nightmare and the possible legal liability if they backtrack on transfusions. There are people who lost loved ones --including children-- because they refused to allow blood transfusions. My mother faced this issue twice in her life and has been fortunate enough to survive both times. She credits Jehovah with saving her, instead of the doctors and nurses who diligently worked to keep her alive with the difficult burden of not using blood.
How will it look if they finally say that they were wrong about transfusions? It has literally been a life and death issue for decades now, and the backlash would probably go mainstream. And I would imagine that at least a few people would sue them, which would definitely get them more attention of the type they do not want. The blood issue is a minefield for them.