If you were to interview a baseball player, you would not ask him how he holds the bat, and how far apart he keeps his feet. Yet, these are the kind of questions people get asked on the interviews - theoretical.
1) There is almost no correlation between theoretical questions and on the job performance.
2) Hiring managers are overly confident that they can determine personality and cultural fit based based on a 30-60 mins interview. All they are really able to determine how well one acted on their specific interview.
Even scientist-experts in such matters as human behavior and cultural fitness require long observations and extensive testing - and even they will tell you that they are often wrong.
Candidates who perform best with such questions are simply able to give us answers we want to hear.
3) In technical professions managers confuse communication skills with technical abilities and knowledge. That is, some of the best developers I knew did not have good communication skills.
4) This is the age of an empowerment and collaboration where individual performance becomes less important. Individual performance still matters, but the collaboration does not get enough focus on the interviews.
5) Many highly qualified people do not perform well in a setting of an interview.
6) Many times I hired people who could not answer any of my questions, and they all did very well. I saw a potential in each one of them.