I can tell you why they have become so easily manipulated. To be a leftist one must be a hypocrite first and a narcissist second. They need to completely ignore their own BS and be able to say with confidence that they still know what is best for you.

Now give them the culmination of mankind's knowledge in the palm of their hands, spoon feed popular opinions, and ridicule or ignore whatever the corporate media doesn't like. The vast majority of useful idiots, or NPCs, have never read The Rules for Radicals let alone how it has been subconsciously implemented and programmed into said individuals by the very programming they consume.

I can get specific but it is self evident, IMO.