I believe the fundamental problem is, most organizations interview in a style similar to testing in college: ask a question about a technical topic, evaluate if the answer is correct. This doesn't correlate especially well to how well a candidate will program if you hire them, but it's the method people learned in school for evaluating someone's knowledge of a topic, so it's what they use. Most developers, and most managers, have almost no training on how to interview well in order to determine who would be a good candidate, so they fall back on the only halfway-similar experience they have.

Now, this raises the question of why our society's method of educating people (or determining if that education has been effective) is not very well correlated to their real-world performance, but that's a whole 'nother conversation.