Two handed stances are a rather modern development.

When you think of shooting now, you are almost certainly picturing the Weaver Stance, the Isosceles Stance, or some modified version thereof. These were developed in the 20th century, and, according to most of what I have read (here is a reasonable article on them) they were really the first stances which emphasized two handed handgun shooting. Its what everyone is taught these days, including military and police. One handed shooting technique is pretty much restricted to point shooting, where accuracy is very much second to speed.

Before the 1950s, one handed was much more common. That was what the US military used for a long time, and it was also the style you would find duelists use, as they needed to present a minimal target to their opponent - you'll still see this in Olympic shooting, where they use a one-handed style. So anyways, the point is that two handed shooting is a rather modern development. In earlier times, presenting a small profile to your opponent was a key concern, and also consider that many shooters would be on horseback, or have a sword in hand! Not to say people didn't shoot two handed before, but the dominant style was one handed, and we should expect to see that reflected in films set in that time.