Board Thread:Naruto Discussions/@comment-25442883-20170422122145/@comment-25122992-20170424145631

Well, I think that's not the main reason, since otherwise any Sharingan wielder would see through the wood clone with ease. However, Madara called himself the only person who could differentiate between Hashi's wood clones and his original body during their lifetime, which means that even all the Uchiha from his clan who surely faced Hashi quite often weren't able to do the same.