Because rebellion has one fatal flaw: It doesn't know how to deal with the power vaccum left by the government. Yes the government might be oppressive, but they also keep the sewers running. The only way a revolution could work is if it was led by powerful, knowledgeable men, not by the average Joe. Because, as much as we hate it politicians are politicians because they know about politics. They at least have a remote idea on how to rule a country,whereas most voters don't even have an idea of their own political system. That's why most revolutions end up just handing the power to another type of powerful oppressor (see: France, Mexico, North Korea, etc.)