Because working out what you think into a string of words that not only makes sense but translates intent, belief, opinion, etc. is not easy.  It’s a rare thing to be able to get out everything that you want to say in a short blurb because something is usually lost either in the writing or the reading.

How people read what you have to say is just as important as how you write what you have to say, and there’s no real way to control that.