The ITBS/TAP are what are called "norm-referenced tests." This means they are designed to sort and rank students on a bell-shaped curve -- in which only a few students score very high, only a few score very low, and most score in the middle. The tests are also designed so that half the students taking the test will end up below average, and half above average. This guarantees that half of the students will always score "below average" on such tests.
If the driver's test were used to sort or rank people, it would have to include some questions not everyone would get right. In such a case, it might ask, "How do you get from Union Station to O'Hare Airport?" or, "What is the chemical composition of diesel fuel?"
ITBS/TAP tests also include some questions which are designed to sort out kids.