I think it's because while it's not exclusive, creators tend to make characters that are generally similar to themselves. Hence why people MOSTLY create characters of the same ethnicity, handedness, etc... Chances are the left handed characters people have reported (which are a minority) were created by someone who was left handed, or at least the artist probably was.
One fun fact (which I've mentioned before)
If you ever take pursuit training one thing they teach you is that if your chasing an untrained suspect (or someone your not sure enough) and lose sight of them where there is a choice of directions ALWAYS turn left.
The reason for this is that most people (like 70%) are right handed, and handedness does come from which side of the brain is dominant. People tend to think towards the direction of their dominant side instinctively. However a person wanting to evade pursuit intentionally thinks counter intuitively i.e. the direction that feels sneaky to them is to turn left.
Thus while not guaranteed this increases your odds a bit since your thinking like a person who is running away so to speak.
Now when dealing with someone who understands this it becomes 50-50 of course because of circular logic... you know will the guy turn right because he expects me to go left? or turn left anyway because he thinks I'll think he'll go right so he'll still go left... ad infinium.
Veteran video gamers might remember the old "follow the right wall" trick for navigating mazes in RPG games and such. That was by and large popularized by right handed people, and can work just as easily in reverse. While differant it relies on a similar kind of logic. I still remember when that was new and that was the default advice for people lost in like the old SSI "Gold Box" AD&D games.
Rambling and off topic, but this topic made me think of this stuff.
