The argument in publishing industry (about papers and textbooks) is that if you cannot afford to buy/rent at the current market value then you still can use a public/university library to get it. This became actually more of a cliché than an argument over time. Now with a significant portion of textbooks (and books in general) become mainly E-books, the industry limited library capabilities and required pay per lend…
If I buy an ebook, can I give it "used" to a library? I would like to, but I don't even know if that's a thing. (Let's assume for the sake of the question that the book I buy is also DRM free.)
In theory, a publisher could sell you an ebook, declare that you own it and can transfer it (like a digital right of first sale) as long as you don't keep a copy.
In practice, it would be a hassle for libraries to verify that permission, so even if you had such a book, they might say thanks but no thanks. Essentially all ebooks are sold under license that each book is for your use only, and no transfers are allowed. Because ebooks are licensed, and not sold complete with a right of first sale, retailers can set whatever conditions they want depending on who they sell to, and the market can't arbitrage. That's why libraries have to pay more for an ebook they're allowed to lend 10 times than you have to pay for the same ebook on Amazon.