The issue is that there are a number of accounts of Cyrus's death, all of them mutually exclusive. Herodotus may have relayed the version about losing against the Massagetae because it suited Greek notions of hubris - that even divinely ordained and immensely skilled men would be brought low by their own confidence, when victory is granted by fate, not human hands. If memory serves, Cyrus, in Herodotus's account, ignores several warning signs and omens, and presses on with the campaign regardless of these 'obvious' signs from the gods.

On the other hand, considering that Herodotus, Father of History and Father of Lies, was basically trying to piece together the world's first truly coherent narrative of world events across a vast gap of geography, languages, and time, in a period when travel was slow and dangerous, he may have just thought that that particular story was the most plausible rather than having any particular prejudice. Other than the general one against Persians as a Greek, considering the two ethnicities' then-recent history of warring.

One thing I will note, though - while in general a chill guy, Cyrus the Great definitely expanded his empire through numerous wars. The thing is, many of his wars also included skillful appeals to the people he was conquering, which both created an advantage during wartime (as the hostility of the locals was often greatly decreased by an argument of "We are here to liberate you, and my NOBLE SOLDIERS are going to act like it") and in the ensuing peace, by minimizing bad blood, so to speak, and limiting the antagonism of the war to that of one ruling class against another, rather than a foreign peoples against a native one.

Considering that Cyrus was praised as 'father' by many peoples whom he conquered even hundreds of years after his death and when the Persian Empire no longer controlled those areas, usually not how the conquered remember their conquerors, clearly the novel technique had some success!