This follows the exact same pattern as the post about よろしく. Today’s kanji for a familiar word is for いる – 居る. A word I see every day and yet I didn’t know the kanji for it. Why do Japanese people often miss out simple kanji and write difficult kanji when they write? It doesn’t make any sense to me.
This came from the keigo section that I’ve been avoiding in my grammar book. There are tables full of difficult versions of otherwise familiar words. I don’t know half of them but still managed to answer the questions… somehow.