the building project to be carried out next year is ,i think ,not easy to complete in time为什么要用to complete 而不用to be completed

the building project to be carried out next year is ,i think ,not easy to complete in time
为什么要用to complete 而不用to be completed

在某些“形容词＋不定式”做表语或宾语补足语的结构中,句子的主语或宾语又是动词不定式的逻辑宾语时,这时常用不定式的主动形式表达被动意义.这些形容词有nice,easy,fit,hard,difficult,important,impossible,pleasant,interesting等.
换句话说
The maths problem is not easy to work out
在换句话说,原句其实就是
the building project is not easy to complete

原句省略了for somebody，加进去就好理解了。
比如：the building project to be carried out next year is ,i think , not easy FOR THEM to complete in time

这个to complete 是指 the building project
也就是 ithink（it is）not easy to complete ……
→be动词 + to do、

这里主语不是物体，不需要被动啊