That's not the point, the question is about understanding fundamental, abstract computer science concepts and being able to craft simple algorithms. Even if we don't manipulate these data structures directly these days in code, there are "real world" concepts that are very similar to these fundamental data structures such as HTTP redirection chains, various stages of a workflow and so forth. It is due to the very nature of computers that a good developer has to be able to find abstractions in real world patterns and solve problems using these abstract ideas. A linked list (or a binary tree) is a very simple abstract idea and it's a good device for measuring the candidate's skill at solving abstract problems.

Additionally, my view and experience is that unless we're trying to hire a specialist in a niche, domain knowledge (in this case, .NET) is considerably less important than general programming skills and abilities; a good developer with limited .NET skills would still write excellent .NET code, a developer who's very familiar with the .NET Framework but who's poor programming skills would be a liability for the company.