And this is the most important question. Once you start asking these questions other, deeper, questions arise. Only Marxism has a coherent answer to them.
Human beings produce their own means of existence.
We don't just produce things, we produce and reproduce social relations between people. For Marxists, the interplay between the development of the material forces of production and the social relations of production is crucial to understanding history. Because from the very moment human society was able to produce more than that needed for mere subsistence there was a struggle over who was to control the surplus. The relations of production reflected not just the necessary forms of social organisation for work, but the forms of social organisation required to distribute the surplus to one class and extract it from another. Before Marx, historians and philosophers had no coherent way of explaining the distinct phases of historical development.