Also, most college libraries like that are so full of bookshelves that the proper library probably didn’t have the open space or decent lighting that the periodicals room did.
From there it was off to the periodicals room at an Iowa State library in order to propose.
Again, we have no details here so we can only guess as to the reason for the admittedly odd location.
To be sure, Beauty and the Beast has a connection to libraries, and Cara is apparently an aspiring librarian herself according to the comments, so maybe that’s the reason.