Fame
Historians will never reach the same level of fame as their subject matter. Ken Burns, documentarian of all things American history, comes close, but even if you've heard his name you still probably have no idea what he looks like.
It'd be hard for a historian to compete with the rise and fall of the Roman Empire or the French Revolution. Those who tend to get famous usually do it because they make history. People like Winston Churchill, Pol Pot, Karl Marx, and Ptolemy are famous for doing a bit more than submitting some articles to historical journals.