Librarian is not a trade, because the job isn’t ’receive book, hand out book’. That’s what the volunteers and assistants do. Working as a librarian requires constant learning and updating yourself on new information and studying the needs of the library patrons. You can read more about other duties here: https://www.bls.gov/ooh/Education-Training-and-Library/Librarians.htm#tab-2
The trades should be more valued, but the way to do that isn’t by denigrating the amount of education that other jobs take.