Why, ruling the conquered peoples, the Persians tried to rely on the local authorities?

When the Persian king looked at his state, he understood that it would be difficult to rule the conquered peoples alone, since uprisings would constantly occur. In this connection, satrapies were created, which were ruled by local governors. On the one hand, they calmed the people, and on the other hand, they faithfully served their king, since it was he who elevated them to the post of governor. So for Darius 1, an administrative reform was carried out in Persia.