'Don't' is a contraction of 'do not.' When using 'why' you are asking a question that involves yourself and the person you are talking to. 'Don't'是'do not'的缩写形式，当使用'why'的时候，你在问一个涉及你自己和你谈话的人的问题。

Here are some examples: 这里有一些例子： 

"Why don't we go bowling tonight?"

 今晚我们为什么不去打保龄球呢？

"Why don't we pick some fresh flowers?"

 我们为什么不买一些新鲜的花呢？

"Why don't we play a game of chess?"

 我们为什么不下棋玩呢？

"Why don't we save more money?" 

我们为什么不存更多的钱呢？

"Why don't we remember this place?"

 我们为什么不记住这个地方呢？

"Why don't we test this before using it?"

 我们为什么不在使用前先测试一下呢？

"Why don't we try and do it again?"

 我们为什么不尝试再做一次呢？

"Why don't we post our results online?"

  我们为什么不在网上发布结果呢？

"Why don't we gather more firewood?"

 我们为什么不多集点柴火呢？

"Why don't we earn more money?"

 我们为什么不多赚点钱呢？