Are you fallaciously implying post hoc, ergo propter hoc?
I can think of a lot of possible causes for that public perception that are more plausible, and have nothing to do with the ability of applicants to perform well on a written examination.
I also have a sneaking suspicion that the raw statistical analysis of such a test from the U.S. in 1975 would show a lot of intrinsic racial, gender, political, and age biases.
Beyond that, many government jobs in the U.S. still have a qualifying exam. Even elementary school janitors have to take them. I have actually taken that particular test. (Long story.) The questions cover such subjects as how to properly employ a push broom, identifying cleaning chemicals, and what to do when a kid pukes in the hallway.
So what happens is that your exam score establishes a baseline ranking. Then your preference points are added for race, gender, ethnicity, disability, veteranosity, and any additional job-relevant questions like years of experience or typing speed. So if you're a white, non-veteran, able-bodied, Anglo male with no prior experience that scores 100% on the exam, you may be only #37 on the ordered-strictly-by-government-regulations interview list. The hiring agency would have to reject 36 other applicants and show good cause for doing so before even calling you.
Greater familiarity with that process bred a whole lot of contempt. Let's just say that I shudder to think of what government might have been like now had the federal government doubled down on exams in the 70s instead of abandoning them.