Because they cannot. Most people do not understand that we have ruling classes/that they are a thing of the past and that mankind now rules himself by something called "democracy". Have you ever read "Silent Weapons For Quiet Wars"? It's a world war II era classified document that found it's way into the public sphere and was disseminated further, but very few people seem to have read it or even heard about it. It details a system for quiet control over all of humanity through a combination of finance, surveillance and social engineering.
We nominally rule ourselves but however we vote the end result looks much the same. The government that notionally represents the people generally doesn't do a very good job at representing the people. It's said that we get the best government money can buy, which is great if you're the one with enough money to buy it.
Finance is certainly an easy way to keep people in check. Devalue their money, spread the lie that high house prices are good (they are good for a limited number of people but not the average working person), blather on about some concept called "work ethic" whereby the people at the bottom work their tails off in exchange for very little while those at the top reap the rewards, and then blame people for burning out because they obviously aren't working hard enough to succeed.
Surveillance is funny because to an extent it's optional. Go outside the big cities and the cost of installing mass surveillance becomes prohibitive. But give people a fun doodad to carry around and they take it willingly. No need to worry about recording our moves - we do that for you. With social media we even broadcast our plans for you.
Social engineering is the really fun one. I wonder how many opinions have been shifted by the media presenting an alternative reality such that the majority silence themselves because they come to believe they are the minority, while the minority are emboldened thinking they are the majority, such that the balance of opinion completely shifts.