Perhaps historical accuracy takes a backseat to the need for illumination -- nobody wants to watch a movie with people sitting around in a room so dark you can't see what the actors are doing or their facial expressions.
It wouldn't be that terribly dark. Lighting technology may have been primitive prior to the last 200 years or so, but people, being people, don't like sitting around in dark places if they can improvise alternatives. I think we get a bit fetishistic these days about painting the past as overly dark (both metaphorically and, in this case, literally)
Curiously the 2015 horror movie "The Witch", which takes place on and around a 17th century New England farming community, was supposedly filmed entirely using natural light and lighting appropriate to what was available at the time. You can see everyone's face and gestures.
Cameras that can see in dark spaces are quite a recent development (better SNR digital sensors, beating film) which has opened a lot of new possibilities in dark filmmaking.
Watch a 90s movie that shows "night" and you'll easily notice how everything is under strong, but blue, lighting.
