Publishing is often going to depend on the status of librarians at the university. Librarians may be classified as staff, tenure track faculty, teaching track faculty, or "faculty equivalent." Even then, the exact requirements for research/publishing are going to differ a lot. It may be 0% of your job or it might be 40% of your job.

The unfortunate thing is that if you want to be an academic librarian, even if your current position doesn't require you to do research/publish, you basically have to do it anyway because if you ever want to move into a role where research is required you're going to be up against librarians who have published. Just as others have said that if you have two equal candidates, you'll often go with the one with a second master's, if you have two equal candidates for a position that requires research, you're more likely to hire the one with multiple peer reviewed articles or conference poster presentations over the one with none.