Listen to conversation and pay attention to all the uh-huhs, hmmms, I guesses, you knows, and likes. Also notice how people tend to repeat themselves constantly. Imagine how including all these filler words and repetitions in a written piece would stretch out a simple conversation for pages and pages.

That would be so boring, you would go right to sleep—so writers try not to do that even though in real life that is the way we speak.