Busy lives, many people are too focused on work and looking after their family to investigate matters and the elite know this.
Lack of knowledge, most people tend to believe or want to believe what their political bodies tell them, because the alternative is to awful to think about (ie they don't give a crap about us).
Trends, and wanting to fit in.
People tend to poke fun at those who do their own thinking, many get called tin hat wearers when in fact in studies most conspiracy theorists are far more intelligent, and have been right about many conspiracies, thinking for yourself has become taboo.