That is a great question. My answer to it is twofold. One, Marx never anticipated the possibility of a labor movement that could negotiate with businesses to improve working conditions and salaries. That did happen over many years and it ultimately helped capitalism survive because it made working in capitalism more palatable. Two, Marx wrote about the ideological superstructure that capitalism created to maintain its power and hold on society and he underestimated how successful that superstructure can be. Big business spends a lot of time and money creating narratives about how wonderful capitalism is and distributing that narrative through the media. Through those efforts, many people are still unaware of the darker effects of capitalism.