Because when the rebels were able to take over Sardis, they had help from some of their Greek brethren. And it's important to note that the Greeks weren't some type of a unified state. They weren't a unified empire like the Persians were. They were a fragmented group of city-states. You have the famous Athens, Corinth, Sparta, all of these city-states. They shared a common language. They shared similar religion, but they were not one unified empire.