Because there was nothing in the law prohibiting literacy tests, they were used to keep African Americans from voting for over 100 years. It ended this day in 1965 when the Voting Rights Act was signed into law.
The use of that loophole says a lot about the culture of the US from 1850 to 1965. The fact that a law was necessary to close that loophole says a lot about the culture that still existed in 1965.
If you want to know what kind of culture you have in your organization today, look at your policies, rules and procedures. Then look at how people circumvent them. And finally look at how you try to prevent recurrence. Each look will give you a richer understanding of your culture.