Mainly because the test is statistically flawed.
Taleb wrote a rather harsh critical article on this topic: https://medium.com/incerto/iq-is-largely-a-pseudoscientific-swindle-f131c101ba39
https://www.independent.co.uk/news/science/iq-tests-are-fundamentally-flawed-and-using-them-alone-to-measure-intelligence-is-a-fallacy-study-8425911.html

Nonetheless, I think there are some realities in this world which can be explained by the IQ values, e.g. wealth differences within countries and between different countries.