I'm not sure that the reason why some (e.g. official) health information sources keep repeating that isn't just a combination of having an easy explanation and

I'm not sure that the reason why some (e.g. official) health information sources keep repeating that isn't just a combination of having an easy explanation and making a (benign) attempt to induce a placebo effect in unknowledgeable patients. If you either get massively technical about complex things that would make most laymen's heads spin, or shrugged your shoulders and said that we don't really know, you might miss on the potential psychological effects that you can get by projecting some kind of confidence.