Most records simply weren't made to start with, period. A lot of those civilizations and cultures weren't literate. And even among those that were, they didn't

Most records simply weren't made to start with, period. A lot of those civilizations and cultures weren't literate. And even among those that were, they didn't keep many records. There wasn't a tradition of keeping track of history the way there was in later societies. This is a problem even in places that were very sophisticated and had written language, like China. But it's even more of a problem in areas that were largely pre-literate, such as most of Northern and Western Europe, the areas around the Black Sea, etc. There are entire cultures and nation-states as important to history as the Greeks who we know very little about simply because they didn't have the habit of recording damned near everything of importance that happened and eventually writing it down. There is so much of the Hittites, the Scythians, the Celts, etc. that we just don't know and may never know because of that.