When enchanting on multiple worlds, feather falling seems to be an evasive enchantment. I'm not sure if it is intended to be as hard to acquire as it is, but I remember it being much easier than it is now. 

Maybe my experience is limited and I have been unlucky, but enchanting both books and diamond boots took many attempts to reveal featherfalling. (Not just showing in the table itself but actually being applied upon enchanting when the stat isnt shown).

I have also acquired hundreds of books from fishing and not one has had feather falling on it but I have acquired countless unbreaking and mending books.