I never really understood why companies don't just take a non-trivial real problem that they have run into during development. Just ask the candidate to talk it

I never really understood why companies don't just take a non-trivial real problem that they have run into during development. Just ask the candidate to talk it out, see if they are able to at least get on their feet toward a solution or an idea of possible solutions. I've never hired anyone, but I can tell you that I could write a linked list in a handful of languages. I can also tell you that it doesn't say much about what I know (or perhaps more importantly, don't). Problem solving is what is important, more important than ability to write code on a whiteboard.