Firstly, a lot of bias experiments seem really obvious after the correct answer has been revealed. This plays directly into our hindsight bias – also aptly named the knew-it-all-along effect – in which the answer makes us think “oh, I wouldn’t have fallen into that trap”. Well, as the data shows, you most likely would have.
A second reason is that a popular everyday conception of intelligence implies roughly that “more intelligence = more good stuff”. Unfortunately, this simplistic rule fails to work here. Intelligence in scientific terms is cognitive ability, which is computational power. In terms of biases, lack of power is not the issue. The issue is that we don’t see or notice how to use the power in the right way. It’s like if someone is trying to hammer nails by hitting them with the handle end. Sure, we can say that he needs a bigger hammer, but a reasonable solution would be to use the hammer with the right end.
[--] while it is true that more intelligent individuals learn more things than less intelligent individuals, much knowledge (and many thinking dispositions) relevant to rationality are picked up rather late in life. Explicit teaching of this mindware is not uniform in the school curriculum at any level. That such principles are taught very inconsistently means that some intelligent people may fail to learn these important aspects of critical thinking.
In their paper they also tabulate which biases or irrational dispositions have an association with intelligence, and which have not (Stanovich & Stanovich, 2010, p. 221):
Now, some might feel the lack of association to intelligence a dystopian thought. If intelligence is of no use here, what can we do? To be absolutely clear, I’m not saying that we are doomed to suffer from these biases forever. Even though intelligence does not help, we can still help ourselves by being aware of the biases and learning better reasoning strategies. Most biases arise due to our System 1 heuristics getting out of hand. What we need in those situations is better mindware, complemented by slower and more thorough reasoning.
Thankfully, that can be learned.