The Ewoks in ROTJ were descended from the survivors of a ship that crashed on Endor millenia ago, hence why they speak a “primitive dialect” of an existing language. They’ve been there so long that the story of how they got to Endor has become mythology, rather than history, to them; for example, the ship had a protocol droid onboard which survived but later “died”, who has been glorified as a kind of god.
Shut up and take my credits.