Many protected classes have lower average credit scores, so I'm not really seeing the difference here between IQ tests and credit checks in this situation.
Personally I don't think anyone who isn't extending you credit should have access to your report, but that will probably require a legislative change.
That's true but the reason Employers don't use IQ tests doesn't have anything to do with false negatives or them caring about fairness. They don't IQ tests because several protected classes score lower on average on IQ tests, so employers have to prove that an IQ test correlates positively with job performance in order to use them. Most employers don't want to deal with this, so they don't use IQ tests.
Several protected classes also have lower average credit scores. It doesn't matter why, just that they do. Therefore it is likely also discriminatory, and and employer should have to support the assertion that a credit score is an indicator of job performance.
My guess is that there haven't been enough lawsuits to scare employers out of using them yet.