Because the vast majority of human beings have very low intelligence. Humans are animals too, and the majority of humans are perfectly fine with doing whatever they are told as long as they get to live one more day, no matter how horrific the conditions are.

This is why all leftist revolutions need a vanguard party, to guide and educate the proletariat to take correct actions.

Check out some leftist/ML theory sometime and all your questions will be answered. Even in the 1850s, Marx accurately predicted the late stage of capitalism we are experiencing now, even predicting the fascist-supporting liberals we see in blue MAGA today.

Leftism has a weird quirk of always being proven correct.

The answer is that capitalism will always result in collapse of society. The most any individual can do is to organize with other leftist groups and be ready to take advantage of the opportunity when the inevitable collapse occurs.