It seems to me that whatever the original purpose was for dust jackets, books have long since evolved into forms that no longer require them. Nevertheless, most hardcover releases still have them.
Is it just a legacy that bookbinders are reluctant to let go, or do they actually serve a purpose?
Well, they still protect the covers on the book. That’s a major concern for people that collect and keep books. It also makes it easier to sell a book at a used store if it’s in good condition.
Also, I’ve always thought it’s cheaper to print the artwork on the dust jacket. The covers on the book are usually plain with just the title on them.
They explain and entice the reader into purchasing the book. A book without a dust jacket is a plain anonymous uncertainty, unless you’re a huge fan of the author and don’t need an explanation of what the book is about.
Dust jackets are advertising. That’s their purpose. Why should any seller stop doing that? Does cereal come in plain gray boxes?
Oh, yeah. They also protect the books. A bit. Somewhat.
Surely all the information and imagery on a dust jacket can be transferred onto the cover.
Not to speak for the OP (well, a bit) but I think the question is why not print the pretty pictures on the cover itself like a paperback, not do without the pretty pictures altogether.
I think ace has it right - it’s probably hard and/or expensive to print on cardboard.
ETA: Oops! Didn’t see you there! 
I don’t get this at all. What do you mean by “evolved into forms that no longer require them”? Unless you’re talking about e-books, then why should a hardback book nowadays have any less need for a dust jacket than it did a hundred years ago? 
Improved printing methods, cheaper processes, and a disposable culture where protection of a book is no longer as paramount as when they were rare and precious.
It’s still significantly cheaper to print the dustcover than to print the boards.
And some people do not like the dust cover’s in their home libraries, preferring the traditional bookend. If they printed directly to the cover, removing the gaudy art would be impossible.
Textbooks often have a printed cover and no dust jacket.
I think the public considers it to be a lesser quality feature, so even if it saves a few cents, it’s not worth the benefits.
Textbooks have a different cover stock than trade (ordinary bookstore) books do. Although printing on it is easier because of its glossiness, the covers are also far more expensive than the “boards” of regular books. The much higher cost of textbooks allow publishers to absorb these costs in a way that would be impossible for trade books, which are at their maximum price point already.
Dust jackets are vastly superior to printing on covers in every way. They are far cheaper, have superior brightness, enable far more wordage (don’t forget the flaps), allow for a variety of special effects, can be quickly and easily changed as necessary, and display photos and barcodes.
Saying that books can do without them is like saying that with a full-body tattoo you no longer need clothing.
Don’t people who collect books pretty much insist that the dust jacket is in pristine condition, too? I always thought that it was silly to print a flimsy, easily torn cover to protect the book, but then have people expect that the cover remain untouched as well.
It’s pretty silly to expect that comic books sold to kids look untouched and unread, but that’s what collectors pay for. Same with toys, sports cards, old china, and basically every other collectible on the market. It’s the rarity of the pristine versions that makes them valuable.
The original edition of my book had a dust jacket. The later print-on-demand version has no dust jacket, and was much more expensive*. I complained to the publisher (who the hell wants to buy an expensive book ? Besides, the new version had printing errors the first edition didn’t), and now the book comes in a cheaper paperback edition (without, of course, a dust jacket).
So, at least in my experience, a jacketless book with the same cover as a jacketed book was more expensive. Not a good trade-off.
*It also lacked those nifty flaps Exapno mentions. One of those flaps had a photo of me taken by Pepper Mill. The jacketless hardcover edition didn’t have them, and this pissed her off.
Don’t know if this is still the case, but when I was in Junior High School we were required to use paper bags and make dust jackets for our textbooks, because they would be reused over and over again. I think once we got to high school it was not required, but don’t 100% remember.
Well, so far I haven’t seen anyone giving a compelling reason why they should still exist.
The best explanation that they’re cheaper than printing on the cover ignores the fact that thousands of books of all kinds (children’s books, reference books, even the occasional coffee table-type epic book) don’t have them, and are often very cheap to buy new.
Cardboard covers are also printed on both sides, so that eliminates the inside flap argument. In fact, some of the books I own have both a full cover dust jacket, and full colour printing on the cardboard cover.
Covers can also be glossy and so have equal brightness and vivid colour levels to paper dust jackets.
It seems to be a legacy that’s being tenaciously clung to. Perhaps it’s time for publishers to step back and rethink.
They haven’t given you a compelling reason. In contrast, I think the reasons expressed here are perfectly acceptable.
Publishing is in desperate shape and always looking for ways to save money and move more product. Why don’t you just tell them how wrong they all are and why your idea is so much better. I’m sure they’d all change their business model once you set them straight.
The cost argument is the only one I find compelling. Otherwise, dust jackets are annoying, flimsy, and pointless. However, I buy mostly trade paperbacks, so it’s rarely an issue for me.
Then rebut his arguments.
I’ve personally always hated dust jackets for the simple fact that they are easy to lose. It wouldn’t be so bad if they didn’t pack so much information only on them. If they were as hard to take off as a properly wrapped textbook, it would be a lot better.