It's literally brainwashing techniques: if you repeat something often enough from an "authoritative" source then the information bypasses logical skepticism and many (more than half) of people just accept it as truthful.

It's a great adaptation for energy savings actually - e.g. engineers MUST use this principle on a daily basis when working in a team environment, or else nothing would ever get done. Even scientists whose literal job is to question EVERYTHING don't re-examine every single precept every single time (is this water that I am adding now? okay now, I am moving my right hand, but is it really MY hand, in the grand scheme of things?:-P oh no, the thing I just picked up, a second ago, is it still the same thing now?).

i.e. active disinformation is extremely destructive, and most people today seem to have few defenses against it. Especially when religion is co-opted as the delivery mechanism.