The "Why don't" pattern is a very polite, very smooth way to suggest something.

Why don't”句型是一种非常礼貌、流畅地提出建议的方式。

Why don't 课堂 - SpeakingMax英语口语达人

So if there's any systematic bias going on in the way these things get graded it'll smooth itself out across the teaching fellows, so we'll have a fair grading system and things.

所以,如果在评分过程中,有任何系统性误差,都会由助教们尽量纠正过来,这样就有了公平的评分系统

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选