it's not much good expecting him to help (you).you为什么能省略?

help 可用作及物或不及物动词.在这句话里,you指的不是特定的你（们）,而是泛意的人们.所以,这里的you可省略.
另外,虽然没有语法错误,但这句话不符合英文的成常规用法.正确的说法应该是“Don't expect too much that he would help.