Some would dispute that claim about the primary utility of standardized testing. For some, the main utility is that it is a common measure in an environment with inconsistent high school course rigor and grading (unlike, for example, in Canada, where external standardized tests are not used for domestic applicants to universities because high school courses and their grades are considered consistent at the province level).
Also, it is rather difficult to eliminate all “nurture” factors from an IQ test that purportedly measures “nature”. And if such a test were used in granting something desired like admission to a university, the “nurture” aspect becomes greater when the test preparation companies figure out ways to help students boost their scores.