that the interviewer asked me to provide an alternate imperative implementation of the LINQ statement, just so he could see that I actually knew how to implemen

that the interviewer asked me to provide an alternate imperative implementation of the LINQ statement, just so he could see that I actually knew how to implement something like that rather than just use it I wonder why interviewers look for these traits when it is very clear that you'll almost never implement a low level data structure.