There should be a reason for it. I learn things because I need them for my job or I find them interesting, hopefully with some overlap. There's a lot of things to learn in life, and it's rather pointless to learn things for an interview process if it doesn't reflect upon the actual job requirements.

Also, it's not like people know nothing. A good interview process learns both what the candidate does and does not know, how what they know could be useful, and how capable the candidate is in filling a knowledge gap if there actually is one between what they know and what is actually needed for the job. That is of course in addition to learning whether they're nice to be around or not.