“Nietzsche is explicitly relativistic about both moral values and truth, preferring to evaluate claims according to what sort of will to power the claims express rather than according to their objective truth-value.”
Nietzsche didn’t believe in “truth”, just on interpretations which are dependent on a perceiver. He saw that society’s conventional “truths” were imposed firmly by those in power, and when those in power fell, other truths were implemented.
The ancient greek saw nature as a projection or representation of the gods and when the civilization fell, their “truths” fell as well, followed by other new “truths” implemented by new masters. In the western modern era, nature is seen from the science point of view, because the preceding point of view, that of Christianity, was brought to an end. In the christian era those in power were ruined by the fall of the monarchies because of the rising power of science, and therefore gave rise for new masters and modern types of government.
Conclusion: The taking of power from previous masters leaves the emerging masters able to plunge their “truths” on society.