Hypothetically, it could be because those folks have already died or are experiencing effects that genpop refuses to corroborate with the treatment. There’s been a major bias against reporting side effects (not that the process has ever been fully hashed out) and iirc the ‘cine industry is the only one you can’t sue, so any potentially-educational lawsuits that might’ve been are a nonstarter. Not saying these things are confirmed but that there’s definitely room for a lot to fly under the radar.