... is that she or he of they snips everything except that to which she or he or they is replying.
Many people here quote the whole of a post when replying such that the new material is off the bottom of the screen, and with so many hundreds of Usenet posts on a daily basis then it is too much of a palaver to page down so that your bon mots then get deleted without being read.
If following a thread there is little point to reproducing all that has been said previously.