why not与what about与why don‘t you与how about与why not you的区别

Why not +动词原形...=Why don't you +动词原形...=What about doing ...=How about doing ...这几个没有区别,可以换用.都是征求对方意见的,"...怎么样?"没有why not you的说法.例:How/What about going for a walk ...shall we +动词原型？shall we +动词原型？用来征求对方意见也可以. Shall wego for a walk ?我们去散步好吗? =How/What about going for a walk ? 你认为我们去散步怎么样?