There is no evidence that they are not.
There’s no solid evidence that IQ (in a healthy person who has no disability) is inherent.
Anyway, why would a conservative buy into the notion that any behavior - and academic performance is a result of behaviors (studying, investing time and effort) - is beyond the control of a perfectly healthy person? Especially considering that public schools, public libraries, etc., are available to everyone.
It’s all about lowered standards and expectations. An increasing number of black families homeschool and, like most homeschoolers, do very well.
There are entire land masses that tell us they are.