People choose to be dumb. Just like they choose to be lazy.

no psyop is required. biology doesn't like making an effort if it doesn't have to do so. you can see lots of non-human examples of this as well.

getting human beings outside of their default biological impulses to be lazy and not think... takes years of training and work. hence why so few people are able to achieve it. and you can always default back to it if you don't maintain the effort consistently