请大哥大姐帮忙，We're writing you为何不用“to”?

因为write属於授与（与格）动词，you是间接受词（宾语），to可用亦可省。
I am writing you a letter.= I am writing a letter to you. 其他授与动词:
He told me a story.= He told a story to me.
She bought me a hamburger. = She bought a hamburger for me.
She did him a big favor.= She did a big favor for him.
I asked him a hard question.= I asked a hard question of him.
但是，上例中等号右边的句子，句型为 Vt+直接受词+介系词+间接受词，介系词不能省略。
你的问题没有出现直接受词（宾语），视为上例中左右皆可。

人家问的是write不是wait。。。

习惯用法
真的，相信我

比较口语是吧！不确定！英语有些习惯用语是不符合语法的！`

习惯用法。口语式的。

同意楼上