其實patch note裡面還真的有寫
http://na.leagueoflegends.com/en/news/game-updates/patch/patch-522-notes
自己Ctrl+F搜尋一下 sword of the occult
我就不全文翻譯了，這應該不難
...
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.
懶人包：難平衡的道具每次處理起來太麻煩啦，我們決定殺了他們比較快
即使他們目前沒有對遊戲有造成什麼危害
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.
懶人包：我們不想要有綁定少數英雄的利基道具，因為這樣會讓我們在平衡英雄時很麻煩
（然後舉例移除魔尊附魔的例子說我們對這類道具都有謹慎研究過，
我們確定這樣不會對草人打野有不良影響我們才移除他的……嗯？）
從Riot的說法中，我們可以推測是因為疊書能出的英雄多，所以不移除
但是疊劍能出的英雄少，所以移除
聽起來很不合理不過這就是Riot的理由了