Today, students write more words than ever before. They write them faster, too. What happens, though, when teenagers write fast? They select the first words that come to mind, words that they hear and read and speak all the time. They have an idea, a thought to express, and the vocabulary and sentence patterns they are most accustomed to spring to mind; with the keyboard at hand, phrases go right up on the screen, and the next thought proceeds. In other words, the common language of their experience ends up on the page, yielding a flat, blank, conventional idiom of social exchange.
Would that be all students, some students, or most students? Back in my day most kids weren't so great at composition, which is why most of them didn't become writers. Even those who had some ability had to learn how to write skillfully, which took time. In fact, writing is a continuous learning experience.