Why can wild plants do without fertilization?

In nature, each plant grows only under the conditions to which it is accustomed, and in most cases it does not happen that there is only one species in one range of races. This means that individual species receive different nutrients from the soil, and the soil does not become poorer. Plus, wild species are eaten by many animals, whose excrement also enriches the land. And their seeds are needed only for the continuation of the species, therefore their size is not important, and when a person plants them, fertility is more important for him.