Several factors have been mentioned in causing this, most of them coming back to Amazon, Google, and Facebook (especially Amazon) working to reduce their distribution costs and secure profits for themselves at the expense of devaluing the publications themselves. Self-published authors are peanuts at the mercy of an elephant, while traditional publishing houses swallow the additional costs by cutting down on advances and royalties for their authors.
Particularly egregious is Amazon’s willingness to allow third-party vendors to list “new” and “nearly new” books at prices below what they will allow original publishers (including self-published authors) to list them at. This is creating a race-to-the-bottom push in publishing that will have the next great “American” novel being written in India, or Nigeria. Truly American authors will be restricted to celebrities who can sell half a million copies on their name alone, and independently-wealthy dilettantes who only write as a hobby.
An often-made suggestion to deal with this is charging royalties on secondhand books.
I don’t agree in charging a royalty on resale. That’s a whole new can of worms that will enable lawyers to take a vise grip on books, just as they have done with music. Not to mention it won’t solve the problem of Amazon allowing third-party vendors to underbid the original publisher.
What I would like to see is a limitation on copyrights–copyrights are SUPPOSED to enable the CREATOR to enjoy a monopoly on their work, but how does a creator benefit from royalties earned after her death? Either royalties end up with heirs she’s never met, much less determined whether to bequeath her royalties to them, or in the hands of some corporate entity, which is either reaping the royalties (if it’s a cash cow) or forcing it out of the market (in order to clear its list for what may be the next cash cow). Either way, the royalties end up beneffitting someone who hand NOTHING to do with the creation, which is what copyright law is intended to reward. Patent doesn’t last NEAR that long, and the average patent takes longer to develop (time and money) and “publish” than the average book! There’s a lot of good material published in the mid-20th Century that’s going to be lost to time because copyright law allows publishers to suppress it until it’s completely forgotten.
Lawyers are already becoming a problem for authors by defending publishers who slap copyright labels on what should be public domain–if it had ever been copyrightable in the first place. (For example: A fact is not copyrightable, therefore a string of facts that forms a description of a game is not copyrightable, yet the NFL fines “Unauthorized pictures, descriptions, or accounts” of their games with impunity.)
Oh, and about “destroying bookstore returns”: The problem with that one is the cost of returns. That’s why a lot of mass-market paperbacks have these statements about “if you bought this book without a cover”–to save postage, bookstores just rip the front cover off the book and send it back as proof of “unsold and destroyed” while shipping the rest of it off to overstock dollar-store distributors.