We hear many reasons, but the most common thread underlying all of them is that some of the beliefs of the early Christians conflict with current doctrine, which makes them unscriptural in the view of those in authority.  (In essence, this elevates current doctrine above the views of the early Christians who relied on the same Scriptures and had the benefit of the oral teachings.)  There is tremendous resistance to considering a view that is different from our own doctrine, even if the early Christians were unified in their view and used Scripture to support that view.