I interview developers. It depends a lot of how you ask the question. Asking "please write a quicksort on the whiteboard" is a pretty bad way of interviewing, you should not expect your candidates to memorize every algorithm invented.
However, if you explain how an algorithm works, and then ask them to write the code for it, you can check if the candidate is able to translate a description to code, which is an essential ability of any programmer.
For example: "In a quicksort, you take a random element of the list (pivot). Then you put all the elements greater than the pivot on the right part, and all the smaller or equal on the left part. Then you repeat the process on each part (left and right) of the list until you can't split anymore." Then based on this description write a simple quicksort in your favorite language, of course you can ask any clarifying questions about how the algorithm works.
I expect a competent programmer to be able to translate the description of the algorithm to code. Yes, it's true that in real world you never have to code a quicksort. But working with simple algorithm makes things easier at the earlier stages of interviewing at large companies, when you usually only have a few minutes to check if the candidate can write some code. Better, more real-world questions are asked at a later stage, when you have more time, typically on a face-to-face interview.