I can only hope to answer by telling you why I study history. I first began to appreciate the study of history as an undergraduate studying political philosophy at Boston University. But what I soon discovered was that my lack of understanding of history, i.e. the actual historical context in which these writers conceived and executed their theoretical work, made my understanding of their philosophy one-sided. Sure, I knew what they had to say about liberty, or the proletariat, or monarchy or the franchise. Ideas are not akin to balloons hanging from the ceiling of Clio's den, waiting to be retrieved by a Marx, a Mill or a Plato.
Ideas have a history.
They undergo a process of development. They change, are modified, are distributed or are forgotten only to reappear years, decades or perhaps even centuries later. Once I realized this fact it was quite natural that I turn my attention to history itself. I could still study Marx or Mill or Plato. Only this time I could do it from the ground up, so to speak.