My guess is that during MK Ultra, they found that rather than disorienting people with psychedelics, its much easier to brainwash people with social conditioning. We're social animals, and creating a perceived consensus is the most effective brainwashing there is. "Things are real based on their perception as being real," Thomas Burger and Peter Luckmann's "The Social Construction of Reality."

Literally this is the first time I've found my sociology degree to be worthwhile haha.

https://en.wikipedia.org/wiki/The_Social_Construction_of_Reality