why dont 和whynot 区别

why don’t 后要加人 why dont you do.why not 后直接加动词 why not do.
1.Whydon't you come over to our place one evening?你何不找个晚上到我们这里来坐坐?来自《简明英汉词典》
2.Whydon't you come around and see us one evening?你何不找个晚上过来看看我们?来自《简明英汉词典》
3.Whydon't you put your chair forward to get a better view?你为什么不把椅子往前挪一点,以便看得更清楚些?
1.You need a break.Whynot take a fortnight off from work?你需要休息,为什么不休假两周呢?来自《简明英汉词典》
2.Whynot get a diviner to expound my dream?为什么不去叫一个占卜者来解释我的梦呢?来自《简明英汉词典》
3.Whynot call on me tomorrow?你干吗不明天就来看我呢?

一般有why dont we do...和why not to do ...用法稍有不同，意思相差无几