WASD is an incredibly common movement control scheme for video games. I'd go so far as to say it is the predominant four-directional control scheme for video games made in the past 20 years that were made to be played with a QUERTY keyboard.
> being right-handed (like most people), I prefer directional controls on the right hand and action buttons on the left.
It is right-handedness that led to this because it was used in conjunction with a mouse, so all those right handed players had a mouse in their right hand, meaning their left hand was on the keyboard.
If you, as a right-handed person, use a mouse in your right hand and the arrow keys in your left hand, you are very much in the minority. Even for games that don't use a mouse, this convention (and muscle memory) is so established that it makes sense to use WASD, even for right-handed players. However making it configurable is always desirable to accommodate the minority of players who might not want to use WASD for any reason.
If you're not an avid gamer or primarily gamed before keyboard + mouse was common, this might indeed seem strange. But for anyone who's gamed consistently in the past 20 years it is very normal.
Why not ESDF? I don't know why initially but today WASD is established convention.