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<p>On internet forums and chat rooms, you write whenever you want to write about something, not when an English teacher or college application asks you to write about something that you are not interested in writing about.</p>
<p>Perhaps the student in question does not like to write about fictional literature (which is the primary context used in high school English writing instruction), but would be fine writing about other things. As mentioned before, stylistic differences in writing on various subjects and in various contexts may also have to do with it. (An internet forum example: know what “TL;DR” means?)</p>