The problem is that an intelligence test can be a double edged sword. Cuts both ways.

First because some of those tests were not really smart in retrospective: False positives tagged as stupid that maybe just had a bad day or did not understood the questions by cultural reasons. Some years after, unsurprisingly, there is not any correlation between the results of the test and the success of this men and women.

And worse, because being tagged as a gifted guy can be a curse. Is an unforgivable sin in some societies. People will start acting resentful and treating you as if you were martian or a danger to them. Is really, really, annoying.