The point is that solving problems, either by inventing new computer science, or more likely formulating a hybrid of known algorithms requires some semblance of problem solving.
A genuine interviewer (and I realize several/many may not be genuine) is solely trying to figure out if the candidate has these types of reasoning skills.
Let me phrase it this way: By asking a common CS question, you'll get people who simply memorize answers/algorithms. By asking something obscure that is rarely known, you can try to get a glimpse into someone's thought process, which is infinitely more valuable than rote memorization.
A genuine interviewer (and I realize several/many may not be genuine) is solely trying to figure out if the candidate has these types of reasoning skills.
Let me phrase it this way: By asking a common CS question, you'll get people who simply memorize answers/algorithms. By asking something obscure that is rarely known, you can try to get a glimpse into someone's thought process, which is infinitely more valuable than rote memorization.