I think the main difference here is how deep and how much detail people want. If someone wants a crash course in a period of history, then watching a couple of documentaries will probably suit them better. Yet, if someone wants a proper understanding of a period of history, then they will need to read a book. People only have the attention span to watch TV for an hour or two, so documentary makers need to squeeze in as much as possible, which means they have to skip things. Books though don't have this problem, and they can cover far more.
I think the main difference here is how deep and how much detail people want. If someone wants a crash course in a period of history, then watching a couple of documentaries will probably suit them better. Yet, if someone wants a proper understanding of a period of history, then they will need to read a book. People only have the attention span to watch TV for an hour or two, so documentary makers need to squeeze in as much as possible, which means they have to skip things. Books though don't have this problem, and they can cover far more.