First of all, because there are too many blind, ignorant people in the world, who can barely handle the events surrounding the nose on their face; and are not adept and aware enough to pay attention.
The perfect example of this are political races. Right now, people don't remember the racist comments Newt Gringrich made while he was chairman of the house, because he has waited through several elections to let the furor of his inflammatory remarks and position die down.
The same stance that brought him enough heat to cause him to resign his position then, he can now cover up and alter, because people have short term memories, so now he has a shot at the white house, which would be tantamount to putting Hitler in office.
The same dimwitted memory problem occurred when GW was elected, and look what that got us. Right now, Jeb is waiting in the wings, claiming he will not run for president, but let another 2-3 elections go by, and I guarantee, he will run, and people who don't know how racist he is, and how much he discriminated and tore Florida up, will be running to the polls to elect him too.
By the way, I am an independent voter, so don't think I'm democratic. I just don't believe in basing my vote solely on 2 issues, and claiming the "lesser of 2 evils" as my motto.
I have also discovered that the average person only seems to respond and react to things that are happening in their own little world, which usually does not exceed a 5-10 mile radius from where they live and work.
Business people have a bit more of a broader range, but they are too busy and stressed with business to keep up as well as they'd like. Entrepreneurs and wealthy business people have advisers that they pay to keep them informed; therefore, if any of the theories out there stand to cost them money or influence, they pay other agencies, like media outlets to spew propaganda to the more ignorant masses to cover it up. That's my spin on it.