I have sifted through everything from piled up junky independent book shops, to cast offs from research libraries, to dumpsters of end of life books. Most books really are not worth the paper they are printed on.

> Most books of value don't get destroyed or thrown away.

Of value to who? Most used bookstores are boutiques that over-curate and will happily refuse or recycle books that they deem are inferior/irrelevant. This is a big reason why I prefer Half Price Books over most any other used bookstore, they sell most everything.