There is, of course, no way to know this for sure. A committed Marxist would give a very different answer than someone who believes in capitalism. Neither can be proven correct.
A committed Marxist would say that the revolution is still coming. They would say it has not happened yet because the ruling classes have managed to trick the workers. They would say the ruling class has managed to split workers on the basis of race and that it has managed to lull them into submission with religion. By doing these things, they have prevented the working class from being sufficiently angry and sufficiently united to rebel.
Someone who is not a Marxist would look at things much differently. From this point of view, there are a number of factors that have prevented revolution. Let us look at three of them. First, there is the fact that advanced capitalist societies have made most of their citizens prosperous. Even today, Americans from the lower middle class up have an amazingly good standard of living. It is hard to make such people want to rebel. Second, these societies have created social welfare systems. These systems prevent most of the poor from being anywhere near as wretched as the poor were in Marx’s time. Finally, advanced societies are democratic. They allow their people to have real input into their leadership and their laws. This, too, makes them less likely to become revolutionaries.
We cannot know which of these explanations is more correct, but most people would see this from the non-Marxist point of view.