The issue about the cover is this: all books are sold on a fully returnable basis. For various reasons, the system to return some books – primarily paperbacks – requires that the bookstore* return just the cover (to save postage). They are contractually required to destroy the rest of the book. Yes, it’s wasteful, but the books have to be destroyed so that the author and publisher get paid for their work. (Hardcovers and trade paperbacks, OTOH, are returned whole).
You can lend or even rent out a book in the US, as long as you are lending an actual, paid-for copy. Books, as objects, are treated in exactly the same way as any other possession: your car, your clothes, your pen, etc. It’s only if you try to copy it that copyright is concerned.
These “naked pulp” books, however, are not actually owned by anyone other than the publisher. Until the publisher (and author) gets paid, then you don’t have ownership and can’t sell it. The book was “returned” to them, so they hold title.
The law does not apply to books that have lost their cover in normal wear and tear. That would exempt most library books, since they have been paid for. In addition, most library books are trade books and thus are never pulped.
Publishers do occasionally sell their paperbacks at a discount. However, they usually punch a hole in the cover. They never sell them coverless because of the possibility of confusion or fraud.
Libraries are also allowed to rebind books (after all, they own them). The issue would be if you had a “naked pulp” book and tried to put a new cover on it. You do not own those, so you can’t legally do it.
*The practice is designed to make it easier for nonbookstores that carry only paperbacks (supermarkets, newsstands, etc.) to get their credit without the expense of shipping the entire book back.