其实patch note里面还真的有写
http://na.leagueoflegends.com/en/news/game-updates/patch/patch-522-notes
自己Ctrl+F搜寻一下 sword of the occult
我就不全文翻译了，这应该不难
...
On a more serious note, let's talk at-large about some items that might not
be real threats to game balance (see: Sword of the Occult) but are still
being removed. The answer is two-fold: design trust, and design clutter.
Design trust refers to an item sufficiently fulfilling its intended role.
When a player sees X item, they should be able to trust that said item is
cost-efficient and can fulfill its expectations. Some items in League just
fall to the wayside (like Ohmwrecker. Every season.) and we try to cull the
herd when possible (usually during preseason), but deliberately keeping an
item undertuned so that it can remain fun but unbalanced is just not
something we can uphold while still preserving a competitive game.
懒人包：难平衡的道具每次处理起来太麻烦啦，我们决定杀了他们比较快
即使他们目前没有对游戏有造成什么危害
This leads to our next point about design clutter. Some items fulfill very
niche roles in League and may not actually be undertuned to a very small
subset of champions. In these cases we're careful to assess the individual
impact of removing said item before taking action. You might have seen this
with the removal of the Magus enchantment, where we had to think hard if
jungle Fiddlesticks was truly going to be useless without his finely-tuned
enchantment (we came to the conclusion of no). Niche items that tie
themselves so closely to a champion's balance do end up skewing that champion
to being dependent on the item to function, and can often ‘hide' real design
problems that we can't get to.
懒人包：我们不想要有绑定少数英雄的利基道具，因为这样会让我们在平衡英雄时很麻烦
（然后举例移除魔尊附魔的例子说我们对这类道具都有谨慎研究过，
我们确定这样不会对草人打野有不良影响我们才移除他的……嗯？）
从Riot的说法中，我们可以推测是因为叠书能出的英雄多，所以不移除
但是叠剑能出的英雄少，所以移除
听起来很不合理不过这就是Riot的理由了