War. Have the Elves get overrun by Orcs a few thousand years ago and their great libraries and records were all destroyed. All they have are fragments and oral traditions of the earlier times passed down from the few survivors. Think about how modern historians constantly bemoan the loss...
I totally agree. They only made 2 binders (doh!). I did like the concept for the later spell compendiums and treasure books. Would have preferred one huge book to 4 smaller ones though.