Because humans only produce like minded offspring, incapable of forming their own thoughts opinions and values. There has never been political tension between generations over schema shifts that also don't happen.
E: big heckin /s in case that wasn't obvious
The point is that CRT is important because white people have often been fed a version of reality that has been heavily edited to make racism seem less impactful than it actually was/is at best.
If Grandma is telling you that people of color were lesser human beings back in the day or "uppity" and all that scholastic history teaches is "Racism was a thing, but then MLK and it all got better!" It devalues the entire lesson.
No it's not. It's not passed down in the genes. It's something you're taught. The people who provided someone's genes (parents) may frequently be the ones who teach them as kids. But, for it to be heritable would mean that the child of a KKK member raised by Freedom Riders would end up racist because it was in his genes.