This is because of its limited powers. If local governments were sovereign, e.g. could execute dissidents and forbid emigration, being local wouldn't help much. There have been very small tyrannies. At national levels there are greater instabilities. Governments can become militarist, tribal or racist, communist or fascist.
Opportunities exist for a class or cause to appropriate all of society's resources.
Modern communication makes possible of worldwide ideological instabilities. I suspect that some people will think that these aspects of progress are partly unreal. More to come, including statistics about infant mortality, life expectancy, hours worked, etc. Besides these extensions of past improvements we can expect some entirely new benefits from technology. Human history is one of gradually accelerating progress punctuated by disasters like big wars and worsenings of climate and also periods of stagnation.