There are a number of possible answers to the question of why history has not turned out the way that Marx predicted it would. The answer that a person gives to this question depends to a great degree on the person’s political leanings. Let us examine two different ways in which to answer this question.
First, a person who is dedicated to the idea of capitalism (a conservative) will say that history did not turn out as Marx predicted because Marx was wrong about what people wanted. Marx argued that history was made up of a series of class struggles. He believed that workers in a capitalist economy would feel oppressed and would want to rise up against the people for whom they worked. Conservatives would say that he was wrong. They would say that workers do not feel rivalry towards the rich but that, instead, they want to be like the rich. Therefore, workers do not rebel against the rich but rather work hard so they can become rich themselves. A conservative would also say that Marx did not understand the degree to which workers in a capitalist economy had upward mobility. Because they could climb the economic ladder, they did not develop a sense of class consciousness and did not want to rebel against the rich.
A convinced Marxist would take a rather opposite view. This person would say that history has simply not YET turned out as Marx predicted. Marx did not predict when capitalism would fall and communism take its place. To a convinced Marxist, capitalist governments have been staving off their inevitable fall by doing things providing welfare states to their workers. They have also been using people in other countries as their menial workers, thus exploiting foreigners while keeping their own people happy. Finally, a Marxist might argue that working people are still being mystified by the upper classes who encourage them to unite on racial, religious, national, or other lines. Because the workers are being tricked, they do not develop a class consciousness and therefore do not rebel.
Thus, we can see that it is possible to answer this question in ways that are diametrically opposed to one another. There are also intermediate answers that can be given. For example, a person might say that upward mobility helps prevent workers from wanting to rebel while also believing that the welfare state has moderated the ills of capitalism and made a communist revolution less likely. A person might also point out that the world’s economic system has changed dramatically and that there is much less of a split now between “workers” and “capitalists” since so many workers are in white collar jobs that are unlike the factory jobs of Marx’s day.
The question of what Marx got right is also one whose answer is determined largely by one’s political values. A conservative would say that Marx got very little right. A Marxist would say Marx got most things right. My own view is that Marx was right when he said that capitalism causes tension between workers and their bosses. However, I believe that he was wrong about the degree of tension that would arise and about its consequences.