We know about the Persian empire in the time of the ancient Greeks because the Greeks wrote about them. The Persians didn’t bother.

Much of the Persian corpus of the period is lost to us due to several waves of literary destruction, not because they didn’t bother.

Most Greeks weren’t writing stuff down for history, were they?

As mentioned elsewhere in this comment section, history is not just the events of the past, but how they are arranged into a coherent narrative.