In the Netherlands competing with discount is actually illegal, interestingly enough. The selling price is fixed. Which is a boon for smaller bookshops, but annoying for publishers if the production prices aren't stable.
The unit cost for the publisher to put a $20 AUD book on a shelf in a book shop was about $2 AUD.
The bookstore kept quite a bit of that margin - $10 or so - but they had to pay rent & staff a store. If they were only selling $500 worth of books per day, it wouldn't have mattered if their margin was 100%, the fixed overheads would eat it all. If they could keep stock turning over quickly, the profits were impressive.
None of the books you get through this program are new releases. But they are printed special for imagination library.
Parton did a lot of very nice things and was a great contributor to society in good and decent ways that many of her wealth peers totally fail.
But there has since her passing been an element of myth and folklore that has elevated those accomplishments beyond reality.
Her library is a great idea and her support was notable, but the funding in large part comes from government grants and other donors.
To a large degree, the library program is also your tax dollars at work.
I can also walk into the library and there will be a shelf of free childrens books. Not used, brand new. Stacks of them to take home and keep.
The engine already existed, our public library system.
How good one's library is depends on how well-off the operating local government is. The Imagination Library is more egalitarian because it's often funded at county and state-level, so kids with underfunded libraries get the same level of access as other kids from wealthier zip codes