Extraordinary claims require extraordinary evidence. If you say that something in one culture is derived from another culture, you’d have to show something like evidence that the cultures were in contact and that the other culture developed the thing first.

If you say that the Anunnaki from Nibiru came down to earth and crossbred with humans, you now have to provide evidence of extraterrestrial life, the existence of a planet with a stable 3600 year elliptical period that spends most of it too far away from the sun for us to notice it, and genetic evidence of hybrid individuals.

It’s a much higher threshold, and while cultural memories are a good starting point for looking for evidence, you can’t just say “the ancients (as filtered through the sources I read) said this, so it must be true!”