Formerly, all books that were returned by a bookstore to a publisher had to be returned intact. This led to huge shipping costs, so most publishers agreed to accept just the front cover torn off a mass-market paperback. Most bookstores throw the stripped copies away, after damaging them to such an extent that they can't be resold (which is illegal). Some let their employees take home a limited number of them. Recycling them would be a good idea, but that hardly ever works out because of prohibitive costs and the introduction of yet another tier of people into the mix who might purloin the stripped books and distribute them to friends and family.