Why I cannot find CForm builder in yii2 
Why I cannot find CForm builder in yii2
Why? I guess, because you have not read documentation of Yii 2.
http://www.yiiframework.com/doc-2.0/guide-index.html
There is no "CForm Builder" in Yii2.
Regards
MetaCrawler: he is saying that he can’t find the equivalent of form builder in Yii 2, and he wonders why?
I didn’t use form builder in Yii 1, so I am of little use…
If you are interested in a form builder for Yii 2, then the only one that I can think of is this -> http://demos.krajee.com/builder