To be successful a revolution does not only have to create a mass sense of injustice at the unfairness of the current situation but also a highly organised replacement.
This is what invariably goes wrong. The mass popular uprisings of the communist era were hi-jacked by highly organised groups who stepped into the vacuum, simply took over and proceeded to replace one corrupt system with another that is equally as bad but favoured a new different elite.
A good example of this is the Egyptian uprising. The people rose up and used social media to coordinate protest. It was very effective at gathering people together in large numbers but lacked any structure and organisation. The only two groups with structure and organisation were the Muslim Brotherhood and the military. So Mubarak was displaced but not replaced by a fair, democratic government representing the interests of the people. First we had a thinly veiled theocracy of religious extremism and then by an equally bad military junta.
The difficulty in creating a highly organised replacement is extremely taxing. The media and social machinery of the state convinces most people that there are no alternatives and that it cannot be done. According to them all the alternatives are doomed to failure – as supposedly proved by history. In reality surveillance of revolutionary groups prevents them getting off the ground.
The end result is that most people come to grudgingly accept their lot as minions and paeans in an unjust society, moan and bitch, but believe it is probably the best they can hope for and that the alternatives are worse.
The elite give as little as they can get away with without driving the population into revolt and there is an uneasy stability.