The reason is certainly that Amazon intended the lending feature to be used between a person's small network of acquaintances. This means that the likelihood o

The reason is certainly that Amazon intended the lending feature to be used between a person's small network of acquaintances. This means that the likelihood of being able to borrow every book you want should be pretty low. Lendle gamed this by expanding the set of people with which you share / borrow. At that scale, the feature probably reduced Amazon's sales more significantly than the intended usage.