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Somebody: Enlightened because he didn't destroy most of the local cultures he conquered, but co-opted and appropriated them. Which is why the Hellenistic kingdoms to a large extent continued the history of the conquered culture's, like Persia and Egypt. We call Cleopatra the last Egyptian pharaoh because she was, despite also being a Greek Hellenistic monarch. Again, when the Seleucid Hellenistic kingdom was supplanted by the Parthians, the history of Persia continued, as if uninterrupted.
You could say this was a factor of time, and not having enough of it to replace the existing social systems, but some of these kingdoms lasted for a long time. The Ptolemy's ruled Egypt for almost 300 years. Yet, ancient Egyptian culture was only finally extinguished under the Romans, and especially the Christianized Romans. In India, Greek kingdoms descended from Alexander's armies lasted even longer than that - yet classical Indian culture wasn't replaced by Greek.