It may also have something to do with the fact that the Persian empires were a constant enemy of the progenitors of Western civilization: Greece and Rome. They

It may also have something to do with the fact that the Persian empires were a constant enemy of the progenitors of Western civilization: Greece and Rome. They were an existential threat to Greece, blocked the expansion of Rome, and obstructed the trade routes to China and India. The most significant mentions in the Western canon primarily have to do with the Greco-Persian Wars. As much of European understanding of that time period is filtered through Greek and Roman sources, we hear more about their conquests than their failures.