At some point a test stops becoming a general aptitude test and starts becoming a "how good are you at taking this test" situation. You get specific prep course

At some point a test stops becoming a general aptitude test and starts becoming a "how good are you at taking this test" situation. You get specific prep courses designed just around that one specific test and strategies optimized for that specific test. You start selecting for "elite" rather than "smart." A merit lottery also keeps everybody from having to waste shitloads of time studying for this one test.