why not 后面加动词原形还是-ing形式?

Why not do sth = Why don't you do sth1、你为什么不.）2、你.怎么样?（表示提议、劝诱）Why don't you introduce her to your parents?你为什么不介绍她给你父母?Why not come and see me tomorrow?明天来找我怎么...