There's no reason historians can't incorporate contemporary material in their work. Of course there are challenges in evidence gathering and finding ways to maintain distance from the subject matter, but there are challenges in studying any era of history. However, the premise of the question seems to be that some historians specialize in single years, and that's extremely rare -- if it happens at all. One job historians perform is providing context, and sometimes we provide context for recent events. But we don't (or shouldn't) be describing those events without reference to the foundations they're built on.