The purpose of these classic WoW librams was for their associated quests which awarded Lesser Arcanums that added specific bonuses Leg-slot equipment. The quests - and thus the lesser arcanums - were removed in Cataclysm. However, the librams themselves still exist in the game and are still Uncommon-quality items. They also cannot be sold to a vendor for money. You can try auctioning the libram on the Auction House; you may get lucky and have a collector purchase it. (Yes, there are collectors of items such as these. There are collectors for everything.)
I'm glad these can still be obtained as a loot drop. I'm fond of the reading them for the interesting text and pictures.