The keys I use most are up/down. I tend to move between lines more often than I move between characters. This is true in any editor, but especially in vim, since I almost never move between individual characters, but rather use [w]ord movement commands, or [f] commands, etc.

That's why it makes sense that my strongest fingers are on the up/down motions, whereas to move to the left, a movement I never make, is off to the side.

Also, I wouldn't remap it for practical reasons - hjkl is a standard implemented in many places.