Are directors able to specialize in, say, documentaries, TV shows, or is their work spread across the board?
Sure, most people specialize. In fact, the marketplace wants you to specialize, so they don’t have to think “out of the box” about your capabilities. But oftentimes, jobs come along outside of one’s specialties (corporate or sales, or some documentary genre one hasn’t previously worked in), and one takes the job because it’s new and interesting or, well, ya gotta eat.