Thanks for posting this clarification. It's actually even simpler than that: for white collar employment there's going to be a presumption that IQ is relevant to the job, and there's no procedural hurdle you have to clear to IQ test applicants. The sole concern is, presumably, whether a candidate who is rejected can mount a successful disparate impact claim.

Several household name corporations routinely apply general cognitive tests to candidates. The companies who deliver these tests have logo crawls just like any other SAAS company. If this was a lucrative field for plaintiff's lawyers, you'd expect that not to be the case.

IQ tests aren't more widely used because they're not very useful for qualifying most candidates for most jobs. You generally want to know if a candidate can do the job, not how well they do on IQ tests.