Why don't you 有没有过去时？

我是英语老师，帮帮你。
Why don't you do sth?=Why not do sth?为什么不……？表示“提供建议”
例：Why don't you try it on?=Why not try it on ?
而Why didn' t you do sth?在一般情况下，含有“责备”的意思。
例：Why didn' t you finish your homework yesterday?
你昨天为什么没有完成作业？
至于why do not you..?，不能说全错，但一般不这么说。
祝你进步！

例：Why didn't you go to the party?
当然有过去时，也可以说why do not you...但是听上去怪怪的。还是建议你写why don't you或者why didn'y you

Why don't you有过去时Why didn't you
比如昨天没有去学校上课,老师今天问你:Why didn't you come to school yesterday?对于问过去为什么没有就用过去时,跟一般的词组是一样的!
Why don't you就是Why do not you的缩写,是可以的.就是平时不常用.一般尽量不用why do not you

当然可以啊～
就好象I'm 可以写成I am嘛～
当然有过去式啊～

可以，但是我就觉得Why didn't you go to the party？{例子}较好

可以