Why are you asking a question, the answer to which you already know? Eyebrows are not drawn in order to erase them. For what - the Captain Obvious will tell you. And they wash to cleanse the face before going to bed - so that nothing is smeared and does not stain the pillow. Don't thank.
Usually, such a phenomenon as direct "drawing" of eyebrows is not common, girls simply shade their eyebrows over with a pencil to give the desired shape / density / color to their eyebrows (in particular, if the hair is dyed and the eyebrows are very different in color). Obviously, any makeup is washed off with the rest of the girl's “war paint” in the evening and reapplied in the morning. I don't understand why this routine aspect of the modern life of girls (and often young people) still surprises someone.